My car battery and alternator is good but if my car sits for 6 hrs it wont start

What are you doing to test that battery? If the battery tests good using a Midtronics tester -- the standard in the business -- or a carbon pile tester that can simulate a load for a sustained period of time -- then ok, great. But my guess here is that the battery is in fact not good. Alternatively, there's a rare change that there is some kind of parasitic draw causing the battery to run down in time. I'll say that a battery that goes dead in just 6 hours would have to have a pretty big draw which should be noticeable in other ways, besides specific testing. https://repairpal.com/parasitic-drain-diagnosis That's a quick article about the draw.