Allow to be overridden.

bikeshop_project/core/migrations/0002_auto_20170101_2054.py

@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.7 on 2017-01-01 20:54
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='visit',
+            name='created_at',
+            field=models.DateTimeField(default=django.utils.timezone.now),
+        ),
+    ]

bikeshop_project/core/models.py

@@ -67,7 +67,7 @@ class Visit(models.Model):
         'registration.Member',
         on_delete=models.CASCADE
     )
-    created_at = models.DateTimeField(auto_now_add=True)
+    created_at = models.DateTimeField(default=timezone.now)
     purpose = models.CharField(max_length=50, choices=visit_choices)
 
     def __str__(self):