I'd love a shorter sleeping cycle, too. I find it annoying that just when everything's fine and they finally reached 100%, then... Ohhhh FFS, they're below 25% energy, so another 2 hours waiting around and then wake them - or they will be yet again be delayed at least 1/3 of a day (8 hours) before getting this week's kitten. -Which becomes even more annoying if you're trying to synchronize some couples with each other.
The other requirements for making a box makes sense - hunger, love, happiness - but the energy is just plain annoying, and is the main reason for my cats ALWAYS being out of sync and always ending up giving boxes in the middle of the damn night, even if I carefully made sure they should originally breed at a decent hour.
Once, when I was more in SL and had the time to check in on them all the time, I managed to get a lot of my cats to breed on Wednesday evening. -A while later, that weekly breeding had moved to Friday morning - all due to energy-management. Eventually they bred on Saturday, and then I gave up even trying to synchronize them

It simply takes too much effort, and delays them a little every week anyway.
Sometimes I just wish they could make boxes in their sleep