I work crew for the National Folk Festival (USA) and the late, lamented Washington Folk Festival, where keeping performances on schedule is critical - when you have seven or eight stages running simultaneously, and people expecting to go from one place to another and hear someone in particular, timing is important. We try to keep stages on time by buying a bunch of cheap clocks, and mounting one on each stage where the performers can easily see it. Before an act goes on, the stage manager says "You have to finish at 2:40" - NOT "you have 40 minutes"... then the stage manager usually gives them a 5 minute sign from the wings, too. This helps the performers know clearly what the limits are, and keeps everything going smoothly.