If your aim is the Christmas holiday sales, I think Itch will announce those dates (if they haven’t already), and you can publish your game a few days before that sale starts.
Keep in mind that after you publish a new game, it has to go through some review, and unexpected things might happen, so it’s always best to do things a few days early and have enough time to fix them.
I don’t have any marketing experience on the matter, so I can’t speak about numbers. Hopefully someone with more experience in that area might be able to provide more details.