I logged in Yesterday and opened the Advent Calendar, got my 100 fish Prize, but today it still won't let me open the second door.
Also, I read the requirements for opening the 24th day door, unless you're allowed to open more than 1 door a day, I calculate that it will be impossible time wise for anyone who started the Christmas event to open the door by the 24th of December and claim their prize. Maybe by the 7th of January but not by December 24th.