JW, Dominic Grieves amendment was designed to limit the governments delaying tactics (as much as possible). So - in theory - TM has 3 days after the ‘downvote’ of tomorrows vote to come up with plan ‘B’. So in this respect her ability to delay is limited to 21st Jan.
TM could of course pull tomorrows vote - unlikely IMO but I’m guessing that you still think it’s possible.
But if there is a vote tomorrow then things could happen very rapidly (IMO). Corbyn has to get his ‘No confidence’ vote out of the way ASAP IMO… otherwise extra delay could be caused by him.
BBC Brexit latest from Labour is that there will be a ‘No confidence’ vote if TM is defeated (I presume immediately).