They sleep. They work 12 hours a day (or longer if you have the early bird or night owl ordinance), 7 days a week, 365 (or 366) days a year once you've fully upgraded. That is insane and the developers of this game should be ashamed for promoting child labor like that.
When they're not working, they order furniture. Sometimes Tommy plays with his train set, and Timmy likes his race car track. In the morning ( before work ), they play baseball with Kick's, Leaf, Dr.Shrunk, and Kk.Slider. On Friday mornings, they go to Nooks and eat breakfast. Timmy loves bacon and eggs, and Tommy likes pancakes with strawberry jam.