txfpcoach wrote: Put a time limit on it these could go for days so make it say 1am drop dead most chips win.
A drop-dead time isn't necessary, and probably won't be appreciated.
As long as the blinds increase at a reasonably brisk pace, the tournament won't last too long. You can calculate backward from the total amount of chips expected to be in play in order to determine how quickly you will need to raise the blinds. For instance, if you have 50 players who each receive $1,000 in chips (including all available rebuys), then the maximum amount of chips in play will be $50K. A tournament certainly won't last very long after the blinds increase to where 10-15% or so of the total chips are committed in each pot. So blinds of 2,000-4,000 or 3,000-6,000 will end matters very quickly (in fact, the tournament is fairly likely to end before the blinds even make it that high).
So assuming under the above scenario you start with blinds 10-20, and then progress as follows: 15-30, 25-50, 50-100, 100-200, 200-400, 400-800, 500-1,000, 1,000-2000, 2,000-4000, 4,000-8,000--you could allow a full 30 minutes at each blind structure and still conclude your tournament in about 5 hours. If you have more players, more chips per player, or a combination of the two, you can adjust the timing of the increases (e.g., to 20 minutes per round) so that the blinds constitute a suitably high ratio of the total chips by the 5-hour mark.
The main thing is that you want the tournament to move along at a decent clip while still allowing skill to play a part in the outcome. If the blinds increase too rapidly the tournament basically degenerates into a crapshoot, because players are forced to gamble in order to accumulate enough chips to stay ahead of the blinds.