Only better watches like Forerunner 245-945, Vivoactive 3-4, Fenix 5-6 are supported.
Watch can access internet only once in 5 mins.
Before you log in, it checks every 5 mins.
When logged in, it reads calendars once in 60 mins to save battery (can be changed in settings).
After hiding and re-appearing, the watch updates calendars within 5 mins.
In default settings, battery consumption is better than with original Garmin watch faces (according to my measurements).
Changing a frequency of updates heavily influences the battery consumption. Keep it on default 60 mins if possible.
Strong dial flavor is not supported by calendars yet.
When no calendar set, the watch loads your primary calendar.
You can add more calendars by pasting calendar IDs from Google Calendar settings.
The list of calendars must be separated by a space or comma.
First calendar has the same color as the watch. Second has a different color. The third is grayish. Then it repeats.
I've heard of watches that do not load calendars. Some started to load calendars after reinstallation.
I'd like to fix it, but did not find the cause yet. Write me if you have a problem.
You can help me by sending a debug log.