diff --git a/vizier/_src/pyvizier/shared/trial.py b/vizier/_src/pyvizier/shared/trial.py
index 0bc0d977c..e7f634f3d 100644
--- a/vizier/_src/pyvizier/shared/trial.py
+++ b/vizier/_src/pyvizier/shared/trial.py
@@ -503,12 +503,13 @@ class Trial(TrialSuggestion):
 
   creation_time: Optional[datetime.datetime] = attr.ib(
       init=True,
-      default=datetime.datetime.now(),
+      factory=datetime.datetime.now,
       converter=_to_local_time,
       kw_only=True,
       repr=lambda v: v.strftime('%x %X') if v is not None else 'None',
       validator=attr.validators.optional(
-          attr.validators.instance_of(datetime.datetime)),
+          attr.validators.instance_of(datetime.datetime)
+      ),
   )
 
   completion_time: Optional[datetime.datetime] = attr.ib(
diff --git a/vizier/_src/pyvizier/shared/trial_test.py b/vizier/_src/pyvizier/shared/trial_test.py
index 00653fad1..da33bf987 100644
--- a/vizier/_src/pyvizier/shared/trial_test.py
+++ b/vizier/_src/pyvizier/shared/trial_test.py
@@ -305,6 +305,11 @@ def testDefaultsNotShared(self):
     trial1.parameters['x1'] = trial.ParameterValue(5)
     self.assertEmpty(trial2.parameters)
 
+  def testCreationTime(self):
+    trial1 = trial.Trial()
+    trial2 = trial.Trial()
+    self.assertGreater(trial2.creation_time, trial1.creation_time)
+
 
 class ParameterDictTest(parameterized.TestCase):
 
diff --git a/vizier/pyvizier/converters/core_test.py b/vizier/pyvizier/converters/core_test.py
index 9c862ce03..21903aac2 100644
--- a/vizier/pyvizier/converters/core_test.py
+++ b/vizier/pyvizier/converters/core_test.py
@@ -340,6 +340,7 @@ def test_parameters_and_labels(self):
             final_measurement=pyvizier.Measurement(
                 steps=1, metrics={'y1': 10.0, 'y2': 20.0}
             ),
+            creation_time=None,
         ),
         pyvizier.Trial(
             parameters={
@@ -349,9 +350,12 @@ def test_parameters_and_labels(self):
             final_measurement=pyvizier.Measurement(
                 steps=1, metrics={'y1': 40.0, 'y2': 50.0, 'y3': 60.0}
             ),
+            creation_time=None,
         ),
     ]
     trials = converter.to_trials(actual_features, actual_labels)
+    for t in trials:
+      t.creation_time = None
     self.assertEqual(
         actual_trials,
         trials,