Different places will have different rules but how I've seen it is that it's a reverse dealer button which only moves when the dealer button and the bomb pot line up. When it lines up the player gets to choose if it's a standard hand or a bomb pot hand. The bomb pot button then moves to the counter clockwise person one time and doesn't move again until the dealer button gets back around to it.
Poker houses I've been to also do bomb pots on dealer changes which is every x minutes.
Poker houses I've been to also do bomb pots on dealer changes which is every x minutes.