I came to the forum to see if I was losing my mind as I was sure they were 8 hrs yesterday, but now they're 4 hours. So I guess they took your advice @tigeress!
In case any powers-that-be lurk in the forum I wanted to say I agree that 4 hours is better and promotes engagement with the game (which I assume is the main point of repeatables.)
If the repeatables require high energy as these do, and there's an 8 hour refresh time, most of us (with a day time capacity typically less than 8 hrs) would have to decide to a) use up some energy during the day thereby not having enough energy to do the repeatables later, or b) increase capacity to cover the repeats later and not play during the day (I would choose b).
At 4 hours it keeps me coming back throughout the afternoon and evening to get a little more done and use up my energy to get the 2nd round complete, maybe even a bit of a 3rd round.
@Roeland do we know if there is any benefit to collecting more than the required 180? Equipment? I see nothing in the shop.