Continuity mistake: In the scene when Scrooge is talking to the boy after he changed, the boy has a sled that was right by some posts, but after Scrooge gets excited because he didn't miss anything and we go back to the boy, his sled is now further away.
Continuity mistake: While in Scrooge's office, the businessman on the right is about to write down Scrooge's contribution in the ledger, with his pen close to the page. The next shot shows the businessman's writing hand and pen away from the ledger.
Answer: It's basically the magic of Christmas. While, to Scrooge, three full days have passed, in reality his whole experience took place in a single night, allowing the reformed Scrooge to enjoy Christmas Day.
Tailkinker ★