They get the events from the default calendar module. But the events are broadcast by url separately.

Some will take longer than others.

Ext3 doesn’t want to flash the screen every time it receives a block of events. It doesn’t know when the events will come. So, it has its own refreshInterval time (10 mins default), then it draws whatever it has, and then waits again

But, you don’t want to wait 10 minutes for the first display , so it has a second timer

waitFetch:5000, 5 second wait before drawing any events

If the events arrive after 5 seconds, they dont get displayed til refreshInterval time.

So, you can adjust those two to improve your viewing experience

Note that longer waitFetch means more time after start before any events are displayed

If you use pm2 to launch MagicMirror, it captures the log messages about startup and events being broadcast.
You could examine those time stamps to determine how long each cal Might take, and use that as a guide to waitFetch time

The longer waitFetch means no events are displayed after startup til waitFetch expires

Are the calendars on the same fetch cycle?

We look back a year, and forward maxdays

But the entire calendar is presented