TS4 - Time won't stay in 2 or 3 speed??

My sims game was working just fine, but right after I adopted 2 cats, I was unable to use 2, 3. or ultra speed when the sims are all sleeping. They work fine when they're awake or at school/work-- but whenever I try it while they're all sleeping, it stays in 2 or 3 speed for 10 in-game seconds and automatically goes back to regular speed... which is really, really, REALLY annoying when all the sims are asleep. I have tried to create a new save game, delete their inventories, and even tried getting rid of the cats - nothing has worked. 

Thank you!!