I spoke to the Cardroom Manager at Bristol Gala last night, and I got the distinct impression it was register on the day as he said something like "starts at 2.30 so get here well before then".
I daresay that Gala Bristol will be as in demand as places like Manchester and Edinburgh, not just because it"s new but i"d assume that all those outside the area would prefer Cardiff, but that"s just my 2 cents.