I've posted my buy-back format proposal before, but in case you missed it the first time....
Basic:
Run mini-qualifiers with groups of 8 in a single-elimination format. Once a group starts, it plays continuously until there is one winner with brief breaks (10 min?) between matches. The winners of each group are into the second level. The 7 losers of each group of 8 can buy back if they want.
As soon as you have 4 players ready at the second level, run a 4 player single-elimination to produce one qualifier for the 32-player final level event. Again, they play back-to-back matches The three losers at that level can get back in if they want at the first level. You continue running first level mini-qualifiers and second level elims until you reach 1024 total entries (32 finalists) or you reach a time cut-off.
Some details:
The 8-4-32 grouping could be 4-4-64 or something else.
Early signups could know their group start time weeks before the event.
It's possible to arrive and enter after the start of a tournament as long as more mini-qualifiers are being formed.
It would be possible for one player to enter more than two times if they start in an early group and the cut-off isn't reached.
If the 32-player final bracket isn't filled, the byes can go to the earliest qualifiers to encourage promptness.
Match times would be easy to estimate. It's mostly your group start time (which can be estimated pretty accurately) and then you will play two or three matches back-to-back. For the final 32, it is simply five rounds of single elimination. For the nine ball finals, those five rounds could be scheduled at 11, 1:30, 4, 6:30 and 9 on Saturday. Any 9-ball qualifier started on Friday has to be able to finish on Friday, so there would be a mandatory cut-off time to get a midnight or earlier finish.
The one pocket could start as soon as the bank pool started to wind down, and similarly for the nine ball. You don't need all of the players present to start an event -- 64 is plenty. And the bank pool finalists don't even have to enter the one pocket until their bank pool is finished.
The runner-up in each mini of 8 could get his entry fee back with a corresponding payout for the losers at the second level. That would encourage buy-backs.
The main point for Derby City is that this format has no waiting for slow matches at the end of a round to see who is in the draw. The tables are kept busy. I think they could have 1024 entries in each event.