Hey Danicob, everything was clear in the rules - the timer was pinned to the top of the game jam, consistently showing hours, minutes and seconds left to submit your game to the contest. The timer was set in CET, counting until Central European midnight, as this is the timezone we operate in.
The rules said that content cannot be added starting from December 1st, without specifying the timezone - meaning that you could still add your content to already submitted games if in your timezone it was November 30th. But the game would have to be submitted to the contest by then - there's no option on Itch to change deadline depending on the timezone, the timer always goes down to the shared time for everyone.