How does Rift Incursions' timing work?

it seems like no matter what I do, when I host my private solo server, it is always before a rift 1 incursion, and not like a set amount of time before, but different every time.

countdowns continue when the server is paused, and even when I quit the game.

I tried changing rift incursion settings (duration and interval) but the interval doesn't seem to do anything, usually it just take the largest duration as the interval instead. And when I set duration to the lowest, it doesn't work (trying to maximize rift 2 incursions)

are rift incursions tied to real world clock? what do the settings (duration and interval) actually accomplish?