I realize this film is not to be taken too seriously, but at the beginning, after the time trip, how on earth did the four of them get to the top of the mountain without passing through the ski lodge or seeing anyone else?
And they were all naked in the hot tub, where did they get their clothes/ski gear/etc without noticing their hotel room and things had changed?
Well, figure they were heavily hung over in the morning and possibly got up very early. If we assume that their clothes and gear were not identical but probably very similar, and they wound up getting up fairly early in the morning, they may have stumbled through getting dressed, gotten through a mostly empty lodge without looking at anyone very closely or talking to them other than a few vague mutters that wouldn't have had anything to do with the year ("Four tickets." "Five dollars, please." "Hnnh. (Only that much?)"), and so on. Basically it's only once they got up to the top that they started to be coherent enough to notice things.