I second, third and fourth the suggestion about turning your wrist watch to face the inside of your wrist. Makes it easy for me to keep track of time.
When you are only one of a number of scheduled acts, time IS important; but when you are the single act, time is just one factor. You have to gauge your audience: are they getting tired? this is important when you are playing to seniors! If the audience is enthusiastic and wants more, I generally speak (from the stage) to aske the person responsible if we can play a tune or two more...or if they aren't present, I ask the audience.

Rich McCarthy