Something like this in your crontab should work:
# m h dom mon dow command
- PYTHONPATH=.
- DJANGO_SETTINGS_MODULE=patchwork.settings.production
- */10 * * * * cd patchwork; python patchwork/bin/patchwork-cron.py
+ */10 * * * * cd patchwork; ./manage.py cron
- the frequency should be the same as the NOTIFICATION_DELAY_MINUTES