Hi Dimm!
You can set up activity reminder emails, but at this time they can only be sent out 15 minutes before the due date. We are currently revising this for future versions of Method. There are a few things you need to check to make sure they are being sent:
1. Go to Customize>Tables/Fields and click Edit Table... next to your Activity table. Make sure that Email me reminders for records in this table before they are due is checked.
2. Go to Customize>Users and click Edit... next to your user. Skip to Step 3 of 10 and make sure Send email reminders before they are due is checked. Note that you can also set SMS reminders here.
3. Go to the New Activity screen and click the three dots button next to the Type field (see the screenshot below) to edit your activity types. Make sure that your specific activity type is set to cause a reminder.
Hope this helps!
Jason