diff --git a/src/include/utils.h b/src/include/utils.h
index a068ca09..9e0fc99f 100644
--- a/src/include/utils.h
+++ b/src/include/utils.h
@@ -124,6 +124,7 @@ extern int     copy_int_list(int**, int*, int);
 extern int     copy_strlist(xce_strlist_t*, xce_strlist_t);
 extern void    free_timewindow_config(xce_timewindow_config_t*);
 extern xce_timewindow_config_t* dup_timewindow_config(xce_timewindow_config_t*);
+extern int xce_timewindow_is_open(xce_timewindow_config_t*, time_t);
 extern void free_resource_thresholds(xce_res_threshold_t**, int);
 extern xce_res_threshold_t** dup_resource_thresholds(xce_res_threshold_t**,
                                                      int);
diff --git a/src/lib/meson.build b/src/lib/meson.build
index a7182d46..4e7df5b3 100644
--- a/src/lib/meson.build
+++ b/src/lib/meson.build
@@ -152,6 +152,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_delay.c',
                    'testsuite/test_ordq.c',
                    'testsuite/test_preason.c',
+                   'testsuite/test_window.c',
                    'testsuite/test_kvmgr.c',
                    'testsuite/test_group.c',
                    'testsuite/test_xlist.c',
diff --git a/src/lib/testsuite/test.c b/src/lib/testsuite/test.c
index 9e2d554f..ed855fad 100644
--- a/src/lib/testsuite/test.c
+++ b/src/lib/testsuite/test.c
@@ -14,6 +14,7 @@ extern void test_utils(void);
 extern void test_config(void);
 extern void test_idgen(void);
 extern void test_preason(void);
+extern void test_window(void);
 extern void test_ordq(void);
 extern void test_delay(void);
 extern void test_kvmgr(void);
@@ -133,6 +134,7 @@ int main(int argc, char* argv[])
     TEST(test_error);
     TEST(test_utils);
     TEST(test_preason);
+    TEST(test_window);
     TEST(test_ordq);
     TEST(test_delay);
     TEST(test_kvmgr);
diff --git a/src/lib/testsuite/test_window.c b/src/lib/testsuite/test_window.c
new file mode 100644
index 00000000..96577c65
--- /dev/null
+++ b/src/lib/testsuite/test_window.c
@@ -0,0 +1,133 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#include "unity.h"
+#include "utils.h"
+#include "xce/types.h"
+
+/* 2026-08-15 is a Saturday (tm_wday=6 → our day index 6), 2026-08-16 Sunday. */
+static time_t at(int day_of_month, int hour, int min)
+{
+    struct tm tm;
+
+    memset(&tm, 0, sizeof(tm));
+    tm.tm_year = 2026 - 1900;
+    tm.tm_mon  = 8 - 1;
+    tm.tm_mday = day_of_month;
+    tm.tm_hour = hour;
+    tm.tm_min  = min;
+    tm.tm_isdst = -1;
+
+    return mktime(&tm);
+}
+
+static xce_timewindow_config_t* make_window(int nseg)
+{
+    xce_timewindow_config_t* w = (xce_timewindow_config_t*)calloc(1, sizeof(*w));
+
+    w->nsegs = nseg;
+    w->segs  = (xce_timewindow_seg_config_t**)calloc(
+        nseg, sizeof(xce_timewindow_seg_config_t*));
+
+    return w;
+}
+
+static void add_seg(xce_timewindow_config_t* w, int idx, int day, int oh,
+                    int om, int ch, int cm)
+{
+    xce_timewindow_seg_config_t* s
+        = (xce_timewindow_seg_config_t*)calloc(1, sizeof(*s));
+
+    s->open  = (xce_timewindow_time_t*)calloc(1, sizeof(xce_timewindow_time_t));
+    s->close = (xce_timewindow_time_t*)calloc(1, sizeof(xce_timewindow_time_t));
+
+    s->open->day  = day;
+    s->open->hour = oh;
+    s->open->min  = om;
+    s->close->day = day;
+    s->close->hour = ch;
+    s->close->min  = cm;
+
+    w->segs[idx] = s;
+}
+
+static void test_no_window_always_open(void)
+{
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(NULL, at(15, 10, 0)));
+
+    xce_timewindow_config_t* empty = make_window(0);
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(empty, at(15, 10, 0)));
+    free_timewindow_config(empty);
+}
+
+static void test_daily_window(void)
+{
+    xce_timewindow_config_t* w = make_window(1);
+
+    /* every day 09:00–17:00 */
+    add_seg(w, 0, 0, 9, 0, 17, 0);
+
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 10, 0)));
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 9, 0)));
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(15, 17, 0)));
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(15, 18, 0)));
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(15, 8, 59)));
+
+    free_timewindow_config(w);
+}
+
+static void test_overnight_window(void)
+{
+    xce_timewindow_config_t* w = make_window(1);
+
+    /* every day 19:00–07:00 */
+    add_seg(w, 0, 0, 19, 0, 7, 0);
+
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 20, 0)));
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 23, 59)));
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(16, 3, 0)));
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(16, 12, 0)));
+
+    free_timewindow_config(w);
+}
+
+static void test_day_scoped_window(void)
+{
+    xce_timewindow_config_t* w = make_window(1);
+
+    /* Saturday (day 6) 09:00–17:00 only */
+    add_seg(w, 0, 6, 9, 0, 17, 0);
+
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 10, 0))); /* Sat */
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(16, 10, 0))); /* Sun */
+
+    free_timewindow_config(w);
+}
+
+static void test_multi_seg_any_open(void)
+{
+    xce_timewindow_config_t* w = make_window(2);
+
+    /* 09:00–12:00 and 14:00–18:00 */
+    add_seg(w, 0, 0, 9, 0, 12, 0);
+    add_seg(w, 1, 0, 14, 0, 18, 0);
+
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 10, 0)));
+    TEST_ASSERT_EQUAL_INT(1, xce_timewindow_is_open(w, at(15, 15, 0)));
+    TEST_ASSERT_EQUAL_INT(0, xce_timewindow_is_open(w, at(15, 13, 0)));
+
+    free_timewindow_config(w);
+}
+
+void test_window(void)
+{
+    printf("\n>> window test\n\n");
+
+    RUN_TEST(test_no_window_always_open);
+    RUN_TEST(test_daily_window);
+    RUN_TEST(test_overnight_window);
+    RUN_TEST(test_day_scoped_window);
+    RUN_TEST(test_multi_seg_any_open);
+}
diff --git a/src/lib/window.c b/src/lib/window.c
index 08eaf9c6..029de6f3 100644
--- a/src/lib/window.c
+++ b/src/lib/window.c
@@ -1,5 +1,6 @@
 #include <errno.h>
 #include <stdlib.h>
+#include <time.h>
 
 #include "utils.h"
 #include "xce/errnox.h"
@@ -46,6 +47,66 @@ void free_timewindow_config(xce_timewindow_config_t* w)
     kill_timewindow_config(w);
 }
 
+/*
+ * xce_timewindow_is_open — is `now` inside the dispatch/run window?
+ *
+ * A NULL config (or one with no segments) is always open. A segment is open
+ * on the given day (seg->open->day: 0 = every day, 1-7 = Mon..Sun) between
+ * its open and close wall-clock times; a close time earlier than the open
+ * time denotes an overnight window (e.g. 19:00–07:00), which is open from
+ * open-time today until midnight and again from midnight until close-time.
+ */
+int xce_timewindow_is_open(xce_timewindow_config_t* cfg, time_t now)
+{
+    struct tm tm_now;
+    int       day;
+    int       cur_min;
+    int       i;
+
+    if ((cfg == NULL) || (cfg->nsegs <= 0) || (cfg->segs == NULL)) {
+        return 1;
+    }
+
+    localtime_r(&now, &tm_now);
+    day     = (tm_now.tm_wday == 0) ? 7 : tm_now.tm_wday; /* 1=Mon..7=Sun */
+    cur_min = tm_now.tm_hour * 60 + tm_now.tm_min;
+
+    for (i = 0; i < cfg->nsegs; i++) {
+        xce_timewindow_seg_config_t* seg = cfg->segs[i];
+        int                          open_min;
+        int                          close_min;
+
+        if ((seg == NULL) || (seg->open == NULL) || (seg->close == NULL)) {
+            continue;
+        }
+
+        /* day-scoped segment: must match today (0 = every day) */
+        if ((seg->open->day != 0) && (seg->open->day != day)) {
+            continue;
+        }
+        if ((seg->close->day != 0) && (seg->close->day != day)) {
+            continue;
+        }
+
+        open_min  = seg->open->hour * 60 + seg->open->min;
+        close_min = seg->close->hour * 60 + seg->close->min;
+
+        if (open_min <= close_min) {
+            /* same-day window [open, close) */
+            if ((cur_min >= open_min) && (cur_min < close_min)) {
+                return 1;
+            }
+        } else {
+            /* overnight window: from open today until 24:00, or before close */
+            if ((cur_min >= open_min) || (cur_min < close_min)) {
+                return 1;
+            }
+        }
+    }
+
+    return 0;
+}
+
 static xce_timewindow_seg_config_t*
 dup_timewindow_seg_config(xce_timewindow_seg_config_t* src)
 {
diff --git a/src/scheduler/include/sched/types.h b/src/scheduler/include/sched/types.h
index 8b32785e..f876910f 100644
--- a/src/scheduler/include/sched/types.h
+++ b/src/scheduler/include/sched/types.h
@@ -75,6 +75,9 @@ typedef struct {
     int32_t  accept_interval;
     int32_t  sched_delay;
     char*    resreq;
+    /* dispatch window (queues.yaml start_time/end_time); NULL = always open.
+     * Duplicated from the controller's queue config; freed by kill_sched_queue. */
+    xce_timewindow_config_t* dispatchwindow;
 } xce_sched_queue_t;
 
 typedef struct xce_sched_job_ {
diff --git a/src/scheduler/include/scheduler.h b/src/scheduler/include/scheduler.h
index 3d9c8a9b..42aa092b 100644
--- a/src/scheduler/include/scheduler.h
+++ b/src/scheduler/include/scheduler.h
@@ -148,7 +148,7 @@ extern int sched_add_worker(xce_scheduler_t*, xce_sched_worker_t*);
 extern int sched_add_project(xce_scheduler_t*, xce_sched_project_t*);
 extern int sched_job_is_ready(xce_sched_job_t*);
 extern int sched_queue_is_ready(xce_sched_queue_t*);
-extern int sched_queue_status_reason(uint32_t status);
+extern int sched_queue_status_reason(xce_sched_queue_t*);
 extern int sched_commit_decision(xce_scheduler_t*, xce_decision_t*);
 extern int sched_publish_pend_reason(xce_scheduler_t*, xce_preason_set_t*);
 extern int sched_publish_dispatch(xce_scheduler_t*, xce_job_dispatch_t*);
diff --git a/src/scheduler/src/plugins/fcfs.c b/src/scheduler/src/plugins/fcfs.c
index 14cfcbc4..a3dc2507 100644
--- a/src/scheduler/src/plugins/fcfs.c
+++ b/src/scheduler/src/plugins/fcfs.c
@@ -233,31 +233,13 @@ static void* fcfs_elect_job(xce_sched_plugin_t* plugin)
             pendJobs = &(q->pendJobs);
 
             if (!sched_queue_is_ready(q->queue)) {
-                /* Attach the queue-state reason (closed/draining/windowed-out)
-                 * to every PEND job in this queue so a skipped queue explains
-                 * itself (PEND-reason P1). */
-                int qreason = sched_queue_status_reason(q->queue->status);
-                if (qreason != 0) {
-                    ordq_item_t* it3;
-                    for (it3 = pendJobs->head; it3 != NULL; it3 = it3->next) {
-                        fcfs_job_t* j   = (fcfs_job_t*)it3->data;
-                        xce_sched_obj_t* obj;
-                        if (j == NULL || j->job == NULL) {
-                            continue;
-                        }
-                        obj = j->job->schedobj;
-                        if (obj == NULL) {
-                            continue;
-                        }
-                        if (obj->reason == NULL) {
-                            obj->reason = make_pendreason(0);
-                        }
-                        if (obj->reason != NULL) {
-                            add_job_preason(obj->reason->reasons, qreason,
-                                            q->queue->name, NULL);
-                        }
-                    }
-                }
+                /* bug-1521: attaching the queue-state reason to job->schedobj
+                 * here races the allocator thread's MOVE_PTR(obj->reason, ...)
+                 * (sched_make_*_allocation) — same job, two threads, no lock →
+                 * heap corruption (crash stacks land in random capnp/limit
+                 * code). The queue-status reason is reported through the
+                 * scheduler's pending-reason chain instead; do NOT touch
+                 * schedobj->reason from the picker thread. */
                 continue;
             }
             for (it2 = pendJobs->head; it2 != NULL; it2 = it2->next) {
diff --git a/src/scheduler/src/schedobj.c b/src/scheduler/src/schedobj.c
index 48fc10df..cdbc1830 100644
--- a/src/scheduler/src/schedobj.c
+++ b/src/scheduler/src/schedobj.c
@@ -212,9 +212,14 @@ xce_sched_job_t* make_sched_job(void* arg, xce_job_t* j)
 
 void kill_sched_queue(void* arg)
 {
-    if (arg == NULL) {
+    xce_sched_queue_t* q = (xce_sched_queue_t*)arg;
+
+    if (q == NULL) {
         return;
     }
+
+    free_timewindow_config(q->dispatchwindow);
+    q->dispatchwindow = NULL;
 }
 
 xce_sched_queue_t* make_sched_queue(void* arg, xce_queue_t* q)
@@ -238,6 +243,16 @@ xce_sched_queue_t* make_sched_queue(void* arg, xce_queue_t* q)
     queue->accept_interval = q->accept_interval;
     queue->sched_delay     = q->sched_delay;
 
+    if (q->dispatchwindow_config != NULL) {
+        queue->dispatchwindow = dup_timewindow_config(q->dispatchwindow_config);
+        if (queue->dispatchwindow == NULL) {
+            /* treat a failed dup as "always open" rather than failing the
+             * queue — the window is advisory for PEND reasons. */
+            WARN("%s: dup dispatch window for queue %s failed, treating as "
+                 "always open", __func__, queue->name);
+        }
+    }
+
     return queue;
 }
 
diff --git a/src/scheduler/src/scheduler.c b/src/scheduler/src/scheduler.c
index d2448146..899d97f5 100644
--- a/src/scheduler/src/scheduler.c
+++ b/src/scheduler/src/scheduler.c
@@ -1451,8 +1451,9 @@ int sched_job_is_ready(xce_sched_job_t* j)
 
 /* A queue is electable only while it accepts new jobs. The controller
  * maintains q->status (queue.c: closed / inactivated-by-admin); the dispatch
- * window state (QUEUE_STAT_INACT_WINDOW) is not yet computed anywhere, so it
- * is not checked here (PEND-reason P1 note). */
+ * window (start_time/end_time from queues.yaml, retained on the queue by
+ * make_sched_queue) is evaluated here because the controller does not compute
+ * QUEUE_STAT_INACT_WINDOW. */
 int sched_queue_is_ready(xce_sched_queue_t* q)
 {
     if (q == NULL) {
@@ -1462,19 +1463,29 @@ int sched_queue_is_ready(xce_sched_queue_t* q)
         & (QUEUE_STAT_CLOSED | QUEUE_STAT_INACT_ADMIN | QUEUE_STAT_INACT_WINDOW)) {
         return 0;
     }
+    if (!xce_timewindow_is_open(q->dispatchwindow, time(NULL))) {
+        return 0;
+    }
     return 1;
 }
 
-/* Map a queue status bitmask to the PEND reason it should report. */
-int sched_queue_status_reason(uint32_t status)
+/* Map a queue to the PEND reason it should report: status flags take
+ * precedence, then the dispatch window. */
+int sched_queue_status_reason(xce_sched_queue_t* q)
 {
-    if (status & QUEUE_STAT_CLOSED) {
+    if (q == NULL) {
+        return 0;
+    }
+    if (q->status & QUEUE_STAT_CLOSED) {
         return PREASON_QUEUE_CLOSED;
     }
-    if (status & QUEUE_STAT_INACT_ADMIN) {
+    if (q->status & QUEUE_STAT_INACT_ADMIN) {
         return PREASON_QUEUE_DRAINING;
     }
-    if (status & QUEUE_STAT_INACT_WINDOW) {
+    if (q->status & QUEUE_STAT_INACT_WINDOW) {
+        return PREASON_TIME_WINDOW;
+    }
+    if (!xce_timewindow_is_open(q->dispatchwindow, time(NULL))) {
         return PREASON_TIME_WINDOW;
     }
     return 0;