It will be because they don't release the funds until the game has happened.
If the Chelsea game is called off and they have paid you but you want to use your ST for the rearranged game, you can't as you don't own the seat anymore for that specific game. I sold my Watford ticket a few years back and Covid saw the game called off. As they hadn't paid out, I had my seat for the rearranged game and the person who purchased it got given a ticket elsewhere in the stadium. (although the club did panic a little bit and had nothing in place to cover this happening)
Are they saying you have between the 27th and 2nd to request the money or you lose it or the money will be sent within that period?
1st way makes no sense, so surely not. 2nd way will simply be down to whoever is processing the payment and the dates they have given the club. Obviously you lose the 24th/25th/26th as payment days as they won't process a thing on a Sunday or Bank Holidays.
I would be amazed if you are sat on the 10th January and you are still waiting for the money