HA calendar update time

The much-welcomed editing options for the integrated calendar have opened up many possibilities.

However, the docs suggest that the calendar integration is only updated every 15 minutes.

Does this only apply to external calendars, e.g. Gcal, or also the integrated calendars?

I can’t think of a reason for the 15 minutes and this impacts on the calendar usefulness for automation.

So far, I’m noticing that the ‘on’ times for internal calendars are roughly 30 - 60 seconds delayed.