You're an opening act. The boss says, "Okay, we've got an act coming on after you. Please limit your performance to forty-five minutes. Okay?" You answer, "Okay, fine. I got you."
Forty-five minutes pass, you're on a roll, the audience is yours, so you keep on singing, playing, joking, whatever. One hour goes by and the next act is pacing the floor and so is the boss. He gives you the cutthroat sign, meaning finish. Now. You keep right on. Waves of love and joy flow from the audience. You keep right on. Finally after an hour and a half you wind up and give it your all.
Happy with yourself aren't you? Well, you've just committed on of the worse examples of disrespect for the boss and the fellow artist following your long-winded performance. If you were opening for another artist, you've just worn out the audience and he will have to dig himself out of a hole.
If you were in on an evening with two separate shows then you've completely thrown off the evening schedule. Tables have to be cleaned, chairs rearranged, new sound installed etc. The next show is a half hour late beginning. All because your ego wouldn't let go and you don't know about team work and respecting others' time and talent.
The sad part of this experience is that you probably didn't learn the lesson this time and maybe you won't until perhaps you have a chance to open for a major artist and you suddenly have to discipline yourself to stop your performance "on a dime", like after five minutes or ten or fifteen. It won't matter if the audience is giving you standing ovations. Nobody cares! It's show biz. There are rules. Do your time the best you can and get off. This is one of the marks of a true professional artist.