I have this issue as well with Sully, except not AS early. However, I am a 'sleep in till dooms day' kinda person so it really irks me on the weekends when I don't have to get up for work!!
He NORMALLY will sleep until 6:30am... 7:00am a FEW RARE and lucky times. He does however, quite often, think that 5:45am or 6:00am is a good time to wake up. Like this morning. Honestly I just ignore his little fit in there and TRY to get in my extra 30-60mins of sleep. I KNOW he doesn't have to potty and can hold it until at least 630-7am. I learned - I would get up at 5:45/6:00am thinking since he is having such a fit in there he MUST have to go - wrong- he happily goes downstairs, digs through his toy box.. sniffs around the entire house to make sure no 'crumbs' that need hoovering appeared while everyone was in bed.. and will then settle himself quite comfortabley on our couch with a bully stick. He will only ask to go out maybe an hour later, sometimes longer :whistling:. Heaven forbid he chews on the bully stick IN his cage while mommy sleeps.. he refuses. If i try to put him back in with the stick he throws another fit. So when he decides it's time to wake up earlier than the usual time of 630-7am, i ignore ignore ignore. Now he will whine for maybe ten minutes, (instead of the straight 30mins or longer) then I hear an exasperated sigh and a thump and crashing of the cage as he throws himself down in defeat. But he will start whining again maybe 20mins later or make some unhappy grumbles here and there just so I know how unhappy he is. So just stick with the ignoring.. it does slowly get better I have to say.. though there is no way in heck I can sleep in past 7am. Do they ever start to sleep in longer? I am hoping so!! My mom's shih tzus are angels for sleeping in.. they will sleep in with me cureld up on my bed until I get up, till 11am or even 12pm. They will literally not move ALL night.. and I sometimes even get up before them. I don't know what my mother did to them but they LOVE to sleep!!