GOOD NEWS though that you have your plan sorted. But I'd strongly suggest that you see it as a PLAN B and stlll shoot for a plan A that has you arriving earlier, and leaving MUCH later. (Check park calendar for opening and closing times though! Even if the park closes early it'd be nicer to hang in Downtown Disney for dinner etc rather than race onto the bus to feel hungry for an hour of travel back to WHolywood and THEN have to track down dinner there).
Just a few more tips, just my opinion. Have a wonderful time!!
-EDIT- ok me saying they are "bogus in and out times" was a bit harsh sorry, its a fairly good deal but as you note it's a bummer not to stay longer (double check the park calendar though)...just suggest you still look at other transport options cuz it would make a big difference is all. Have a great visit!