UW floors individually fully reset 7 days after that floor specifically had been opened.
So example of you opened b150 on Monday and b151 on Tuesday
150 will reset next Monday
151 will reset next tuesday
however if a floor has no activity for about a day (no players on the floor at all) it will Soft reset. Which means all Entities and Static objects will despawn but the floor layout will remain the same
And I’m pretty sure it does this to prevent the game from eating up tons of memory resource which would cause Lag issues.