The baby squirrels I've helped care for at our Wildcare Center slept and ate most of the day! They were very affectionate, and loved being held and cuddled during feeding time! I'd give him the opportunity to "exercise" but wouldn't be too concerned if he chooses to sleep a lot. Where is he sleeping? As long as he's eating well and seems bright and alert while awake, I think you needn't worry. If the bottle says ok for squirrels, I'm sure it won't hurt him. But do call the center and pick their brains for all the info. you can get. I'm sure you'll need some help re: when and how to introduce him to the wild, once he's ready!