Thanks for fixing the confusion
That was mostly what was happening. I guess it was the active sensors that the alien ships were using that caused the interrupts then indeed.
I say mostly, because there was some buggy behaviour involved as well.
When I turned off automated turns, both the 1-day, 5-day and the 30-day button increased my time by 1 day only.
No events that would interrupt that happened..
Quitting and restarting the game fixed it (the 30-day button gives me 30 days of time progress again)
There's a rather large alien fleet hanging around one of my mining asteroids in Sol now, theire doing some active sensor pinging, but that's all they do.
They don't seem to attack me. They've been exploring my system for 6 months now, first hanging in orbit around earth, then they checked out my terraforming operation on Mars, and now they're admiring an asteroid.