I've had to find and fix this on an installation today ..
If, like mine, all your users will be OK defaulting to one timezone, you can change the default in the database model. I think that, ideally, the application would pick something sensible at account creation time instead .. but this is good enough for me today..
Find the models.py file in django3-mailman
eg, if you installed in a venv, it might be somewhere like /opt/mailman/venv/lib/python3.7/site-packages/django_mailman3/models.py
Find this line:
timezone = models.CharField(max_length=100, choices=TIMEZONES, default="")
and change the default to be what you want, eg:
timezone = models.CharField(max_length=100, choices=TIMEZONES, default="Europe/London")
Now the model needs to be updated, and the software restarted:
$ mailman-web makemigrations Migrations for 'django_mailman3': venv/lib/python3.7/site-packages/django_mailman3/migrations/0003_auto_20210521_1212.py - Alter field timezone on profile
$ mailman-web migrate Operations to perform: Apply all migrations: account, admin, auth, contenttypes, django_mailman3, django_q, hyperkitty, postorius, sessions, sites, socialaccount Running migrations: Applying django_mailman3.0003_auto_20210521_1212... OK
# systemctl restart mailman-web
Test by creating a new account and viewing the profile.