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It's still early days so he may need more time to settle in yet, sleeping all day is normal for a ham, some get up later than others.
He may still be quite nervous so spend time talking to him quietly even if he's in his nest so he gets used to your voice & you being around.
If he's going to have a cage change then it may take him longer to settle again, just take your time with him. When you change over to the new tank put all the old substrate from his current cage in & don't do anything other than spot clean pee for a few weeks so he can get his scent on everything in the cage & start to feel at home.
Does he have any hides or things in the cage which will help him feel safe if he comes out? Too much open space is very intimidating for them.