Give a kid half of an advent calendar and tell them to open the window every second day, let's see how long it'll keep their interest (I expect much less than 12 days) :). That's not how Advent Calendars work!

We’re not kids though…

Let your hair down man, it's christmas!

That was my first thought too, and I'd prefer it, cause sometimes I'll get stuck on a problem, or I'm busy, or I forget, and I'd rather have one more day. Bur it's Eric's call in the end.

Or publish the harder version of the puzzle on a different day to the easier version.