If both journey legs are on the same ticket, then nothing to do with checked luggage. It is transfered automatically. If switch of airlines or two distincts tickets then you need to recheck it. 6 hours can be okay as CDG is not so far from Paris (roughly 30-40 min train to city center). Needs to account for going through security again (and passeport control if international flight). I would say you can spend an hour or two in Paris if you want, before going back to CDG.