What I think would be nice is to have an increment like in chess.
Let's say, for instance, 10 20 meaning you start with 10 minutes and you've got 20 seconds to play your shot each time. If you play your shot in less than 20 seconds, you save the playing time accordingly, and vice versa.
It'd be very beneficial for both parties playing and waiting because the time required to play differs greatly depending on the type of shot you take.