Hard to say with certainty. But probably days, maybe weeks. It depends on how far out of balance the cells are, and there's not a good way to know.
But let's say it 25Ah out of balance (based on the 75Ah capacity). Your BMS passively balances at 50mA, I think. So each hour it can re-balance 50mAh, or 0.05Ah. To get 25Ah at .05Ah per hour, would take 25/0.05 = 500 hours, or about three weeks.
If the capacity is down to 75 AH then I think I am back to trying to answer my initial question of replacing 1 cell and/or looking for suggestions on new cells.
Do the top balance (or wait the three weeks on the charger for the BMS to do it), then do a capacity test. Having the cells out of balance looks and acts like reduced capacity, but doesn't mean that the cells are necessarily bad. You may get most or all of your original capacity back if you blance the pack.
The 'capacity' that your BMS is reporting is the amount of charge from high-voltage cutoff to low-voltage cut-off, but these two things are likely not occurring on the same cell because the pack is out of balance. So cell 3 (for example) cuts off charging because that cell is at 100% charge, but because of imbalance, cell 1 (again, just an example, I don't know which cell is lowest) is only at 75% of charge... Now you discharge and cell one gets to 0% after 75Ah (while #3 is still at 25% charge, but you can't use it), and that's the current 'capacity' of the pack. Balance it, and you'll get more capacity.
