diff --git a/listener/src/api/events-server.ts b/listener/src/api/events-server.ts
index 5695de6..f779878 100644
--- a/listener/src/api/events-server.ts
+++ b/listener/src/api/events-server.ts
@@ -206,11 +206,18 @@ export function createEventsServer(options: EventsServerOptions): http.Server {
               return;
             }
 
+            const executeAt = new Date(data.executeAt);
+            if (isNaN(executeAt.getTime())) {
+              res.writeHead(400, { 'Content-Type': 'application/json' });
+              res.end(JSON.stringify({ error: 'executeAt is not a valid date' }));
+              return;
+            }
+
             const notificationId = await options.notificationAPI!.scheduleNotification({
               payload: data.payload,
               notificationType: data.notificationType || NotificationType.DISCORD,
               targetRecipient: data.targetRecipient,
-              executeAt: new Date(data.executeAt),
+              executeAt,
               maxRetries: data.maxRetries,
               priority: data.priority,
               eventId: data.eventId,
diff --git a/listener/src/services/notification-api.ts b/listener/src/services/notification-api.ts
index 0671201..1894243 100644
--- a/listener/src/services/notification-api.ts
+++ b/listener/src/services/notification-api.ts
@@ -17,8 +17,12 @@ export class NotificationAPI {
     requestId?: string
   ): Promise<number> {
     // Validate input
-    if (!input.executeAt || input.executeAt < new Date()) {
-      throw new Error('executeAt must be a future date');
+    if (!input.executeAt || !(input.executeAt instanceof Date) || isNaN(input.executeAt.getTime())) {
+      throw new Error('executeAt must be a valid date');
+    }
+
+    if (input.executeAt <= new Date()) {
+      throw new Error('executeAt must be a future timestamp — the provided date has already expired');
     }
 
     if (!input.payload || typeof input.payload !== 'object') {
diff --git a/listener/src/tests/notification-scheduler-refactored.test.ts b/listener/src/tests/notification-scheduler-refactored.test.ts
index 251f7f3..a06dd00 100644
--- a/listener/src/tests/notification-scheduler-refactored.test.ts
+++ b/listener/src/tests/notification-scheduler-refactored.test.ts
@@ -258,7 +258,7 @@ describe('NotificationScheduler (Refactored)', () => {
 
       await expect(
         api.scheduleNotification(pastInput)
-      ).rejects.toThrow('executeAt must be a future date');
+      ).rejects.toThrow('executeAt must be a future timestamp');
     });
 
     test('should schedule Discord notification', async () => {
diff --git a/listener/src/tests/notification-scheduler.test.ts b/listener/src/tests/notification-scheduler.test.ts
index 1e51ab1..496cba0 100644
--- a/listener/src/tests/notification-scheduler.test.ts
+++ b/listener/src/tests/notification-scheduler.test.ts
@@ -255,7 +255,7 @@ describe('NotificationScheduler', () => {
       expect(notification!.status).toBe(NotificationStatus.PENDING);
     });
 
-    test('should reject past execution time', async () => {
+    test('should reject expired execution time', async () => {
       const pastDate = new Date(Date.now() - 60000);
 
       await expect(
@@ -265,7 +265,45 @@ describe('NotificationScheduler', () => {
           targetRecipient: 'test-webhook',
           executeAt: pastDate,
         })
-      ).rejects.toThrow('executeAt must be a future date');
+      ).rejects.toThrow('executeAt must be a future timestamp — the provided date has already expired');
+    });
+
+    test('should reject execution time equal to now', async () => {
+      // A timestamp at (or just before) the current moment is already expired
+      const now = new Date();
+
+      await expect(
+        api.scheduleNotification({
+          payload: { message: 'Test' },
+          notificationType: NotificationType.DISCORD,
+          targetRecipient: 'test-webhook',
+          executeAt: now,
+        })
+      ).rejects.toThrow('executeAt must be a future timestamp');
+    });
+
+    test('should reject invalid date object', async () => {
+      await expect(
+        api.scheduleNotification({
+          payload: { message: 'Test' },
+          notificationType: NotificationType.DISCORD,
+          targetRecipient: 'test-webhook',
+          executeAt: new Date('not-a-date'),
+        })
+      ).rejects.toThrow('executeAt must be a valid date');
+    });
+
+    test('should accept execution time 1 second in the future', async () => {
+      const nearFuture = new Date(Date.now() + 1000);
+
+      const id = await api.scheduleNotification({
+        payload: { message: 'Test' },
+        notificationType: NotificationType.DISCORD,
+        targetRecipient: 'test-webhook',
+        executeAt: nearFuture,
+      });
+
+      expect(id).toBeGreaterThan(0);
     });
 
     test('should schedule Discord notification', async () => {