Hi
I've got a chipmunk who spends most of her day in her nest, it's getting better as time goes by.
It sounds like your chipmunk is quite new to your home, so I think he is just a bit disorientated. Most of mine are very active, but only in the day, retiring to their nest this time of year at about 5pm. I have one young chipmunk (Dove) who was having a hard time mixing with the others. So, I've put her in her own aviary. She hardly came out of her nest box for the first month, only once or twice a day. Things have improved in the second month, as she has started taking nesting material back to her box, and now comes out about four times a day. She is not very active compared to the others though. Indoor chipmunks will not hibernate, and carry on through the winter much the same as in the summer. Summer heat can slow them down, but they're most active morning and late afternoon.
Try to make his aviary as interesting as you can, with plenty of places from him to hide in. I look for cardboard tubes being thrown out, chipmunks love these in their aviaries. Tubes with about a 6cm diameter are most popular. The ones inside kitchen towel and toilet rolls can be to small when they get bigger. Also put a deep pot of damp potting compost in his aviary, most chipmunks love to dig. Some of mine like wheels, whilst others never go on them. If he's more than a few months old you can put a towel in the aviary, all of mine love towels or dog blankets. If he's very young his claws will get stuck in the loops of a towel, which is something you need to keep an eye on.
After your chipmunk has settled in to his new home (about two months) you can start to let him out for a run around the home. I'm going to start doing this with Dove, I'm hoping this will bring her out of her shell. Letting them out for a run is the quickest way to tame them, as they get used to you much quicker. Whilst yours in in the avairy, when he does come out, try to talk softly to him to get him used to your voice. My all respond very well to being talked to. All my chipmunks are completely different from when they were young, for some it's taken nearly a year to get them tame, and rushing about.
They are not great eaters, I throw away more fresh food than they eat. They need about 30g of Supa Chipmunk muesli a day. I put out several small dog sized bowls (about 15cm across) of dry food. They will go for the best bits first, so I only change the dry food every four days. I put out a varity of fresh fruits each day, although it's claimed that Supa Chipmunk muesli has everything they need. They are very small eaters, and picky too. They are supposed to like bananas but none of mine with touch them. Mine like sweet corn on the cob, grapes cut in half, pomegranates, the seeds from apples, a butter squash cut in half and blueberrys. They also like a bit of lettuce, but not to much green leaves as it can give them the runs.
I've found that you cannot over feed them, they will nibble only a tiny bit of half a grape, then leave it, maybe to come back later.
I've found that mine don't like any noise where they sleep. Although they mostly go to their nest by about 5pm, they seem to remain awake until about 8pm or 9pm. The old cathode ray tube TV's tend to hum at about 60 KHz, although we can't hear this hum, it does upset chipmunks. If you have an LCD or Plasma TV you will be OK as far as hum, but they still won't like the sound of a telly in the same room as they sleep. During the day when they are awake they don't seem to mind nosies.