diff --git a/swh/scheduler/simulator/__init__.py b/swh/scheduler/simulator/__init__.py
--- a/swh/scheduler/simulator/__init__.py
+++ b/swh/scheduler/simulator/__init__.py
@@ -104,31 +104,40 @@
 
 def fill_test_data(scheduler: SchedulerInterface, num_origins: int = 100000):
     """Fills the database with mock data to test the simulator."""
+    from random import randint
+
+    from swh.scheduler.utils import utcnow
+
     stored_lister = scheduler.get_or_create_lister(name="example")
     assert stored_lister.id is not None
 
-    origins = [
-        ListedOrigin(
-            lister_id=stored_lister.id,
-            url=f"https://example.com/{i:04d}.git",
-            visit_type="git",
-            last_update=datetime(2020, 6, 15, 16, 0, 0, i, tzinfo=timezone.utc),
-        )
-        for i in range(num_origins)
-    ]
-    scheduler.record_listed_origins(origins)
-
-    scheduler.create_tasks(
-        [
-            {
-                **origin.as_task_dict(),
-                "policy": "recurring",
-                "next_run": origin.last_update,
-                "interval": timedelta(days=64),
-            }
-            for origin in origins
+    maxts = int(utcnow().timestamp())
+
+    while num_origins:
+        batch_size = min(num_origins, 10_000)
+        origins = [
+            ListedOrigin(
+                lister_id=stored_lister.id,
+                url=f"https://example.com/{i:04d}.git",
+                visit_type="git",
+                last_update=datetime.fromtimestamp(randint(0, maxts), tz=timezone.utc),
+            )
+            for i in range(num_origins, num_origins - batch_size, -1)
         ]
-    )
+        scheduler.record_listed_origins(origins)
+
+        scheduler.create_tasks(
+            [
+                {
+                    **origin.as_task_dict(),
+                    "policy": "recurring",
+                    "next_run": origin.last_update,
+                    "interval": timedelta(days=64),
+                }
+                for origin in origins
+            ]
+        )
+        num_origins -= batch_size
 
 
 def run(