Something like 50% of the people in Norway watch this on "little Christmas eve" - December 23rd. For a lot of people, this is what officialy starts off the Christmas vacation.
Edit: Source: I'm norwegian and have watched this sketch with my family every single year since I was born.
I'd heard of it as a thing some years ago, but never actually saw it "in the wild" until I was skiing in Norway over Christmas a few years ago. The hotel had it on in one of the lounges, which filled with a variety of nationalities to watch it, notably lacking the British. We're quite mystified.
In fact, one year they were forced to put it on twice, as it was shown as part of a variety show, and was moved earlier than billed, causing an uproar when people realized they'd missed it.
Edit: Source: I'm norwegian and have watched this sketch with my family every single year since I was born.