usually the lines don't go up past 30 minutes ,were going then, but its not deserted there are people there but not a 60 minute line in wait crowd i mean i went on space mountain last time with a wait of 15 minutes! (note: ill never go on it again!) but there will be longer waits for big rides like splash,space,pirates,RNR,TOT and in MK most fantastyland rides in the morning is the best time to go on big rides because most people are in fantasyland also i advise if there is a extra hour to use it so when your in mk you can do most of the rides but usually all of the parks don't have long waits i think the longest we've waited in dec is 25 minutes and that was for GMR but last time star tours was walk on and most of rides like that are but let me be one to warn the Backlot does have a long line even in low time just a little advice and little look into what is going to happen anymore questions just pm me or ask on this thread for the last few years we've gone in early dec and had a wonderful time like spending 5 minutes with characters! Hope i helped!
Splash