Erm... I usually open the game in the morning as soon as I open my pc, check them every now and then while I'm mainly working. Then at nights, I switch to day time again and play with them for some hours. After that I pause the game and close till next day.

They tend to be tired at evenings (their evenings). I noticed that if I switch to day time when they begin to get tired they recover quickly and since the last update I never had any issues with the energy level.