There's no need really too worry. If he gets out in the sun 3-4 times a week is good enough or you can provide artificial uvb.
When fall rolls around, my torts, leopards, don't want to go out even on the nice warm days or if they do, they don't stay out as long as they do in the summer. For not being a hibernating species, they sure act like they like the sleeping part of hibernating. LOL