if it's a standard wheat beer, with cranberry added, you should be fine with a 3 week fermentation, but you are the only one who can check that.
if your SG hasn't changed for 3 days you are done, whether it's 3 weeks, or 6 weeks, that's the indicator.
as far as being ready for christmas, i just bottled a wheat beer on Saturday, and I'm expecting to drink it for New Years (actually on January 7 for the football game), but not for Christmas.
wheat beer doesn't need secondary, but it does like a little extra time in the bottle.
In the fermenters: nada
In the bottle: nada
In the fridge(and the glass): nada
On Deck: anything i can think of