Well I am responsible for planning the sets for my group. If we are performing in a folk club, you can rely on the club MC to signal when there's one more song to go. This is the case in festivals too. But the exception in our case is when we have pub gigs or do the occasional charity gig, it is then that I do check my watch as discreetly as possible. But that is only when we come to the last but one song in the set. Though I say it myself, my timings have proved to be fairly accurate!I put this down to my radio days when I had to be "spot on" with timings in my show.

Yes, I do think that openly checking the time during the performance
gives a bad impression.