As it's an Advent Calendar I definitely think you need to have it as an early birthday present. Lots of little gifts in the build up to your birthday will be amazing. Better than having to open a lot of windows at once.
Open as an advent calendar from 1st December, that is the purpose of them after all!
I got my Kiehls one yesterday, and as much as I'm tempted to open a door, I know it'll be a slippery slope and I'd want to open more...besides, my husband has banned me from opening it! 😋
I know its the the right decision, because if I opened it now I'd be disappointed on Dec 1st. I know the contents, but I like the suspense of what's behind the door, as I don't know what number things are behind.