We would like to organise a simultaneous exhibiton at our chess club, but as we only have the room booked for 2.5hrs, we fear that it might not be over in the given time. I've heard about clock simuls, but I haven't found any "rules" on how to set the time control for each player. I'm assuming that the exhibitor should have a lot more time than the challengers (as he needs to spend time at different boards while all his clocks might be running simultaneously) but I don't know how much time would be fair to set (given that the simul should last for 2hrs, for example). Do you have any suggestions?
A chess simultaneous display is where a strong player takes on more than one opponent simultaneously. Sometimes this is done with clocks but more usually without, when people must move when the simul giver arrives at their board.
Source: Chess Simul – Advice on giving and taking part, emphasis is mine
I would suggest using a single (normal) clock for all games. If a player (not the simul giver) has not ended their game after that time limit expires, then they lose on time. In this system, the simul giver cannot lose on time.
I would also advise that there is an arbiter present to prevent unreasonable delays when the simul giver comes to a player's board. In some simuls, a player is allowed three passes when the simul giver arrives at their board.