Assuming that there is one time zone along the Date Line that has some weird Daylight Saving practice in December that no other time zones follow, that would still mean the maximum difference between any two time zones at any given time is 25 hours (not 50 hours).

Given the most liberal definition of Christmas Eve as the 12-hour period from 7 p.m. on December 24 to 7 a.m. on December 25, that's a 12-hour span in any time zone. Plus the hour gained as he travels through each of 24 or 25 time zones -- that totals, at most, 37 hours that Santa has been away from the North Pole.

Think about it this way: If Santa has a pocket watch set at North Pole Standard Time (AKA Greenwich Meantime), what time will he start his deliveries so that they begin after 7 p.m. Christmas Eve at the Date Line? And what time, by Santa's watch, will it be when he delivers his last gift before 7 a.m. Christmas morning?

That is, if Santa is always on London time, how many hours will have passed on Big Ben between when Santa delivered his first present and his last? I say, at most, 37 hours would have elapsed. (i.e., if you are sitting on a bench looking at Big Ben, and Santa calls you to say he has just started his first delivery, then you will be sitting on that bench looking at Big Ben for less than 37 hours before Santa calls you again to say that he's done.)