What did the neanderthals do in the day time?

Pretty much what you would do if you and a bunch of friends were dropped in the middle of prehistoric earth; make sure you had shelter for the night, keep an eye out for predators, find or collect water from a source, gather food and other resources your camp needed like wood, hunt for meat and fur, sleep, and spend time with one another to keep the stress of uncivilized life from getting to you all.

All of the above takes a lot more time (enough to fill the whole day) when is just you and your own ingenuity.