Pretty good rule of thumb is that if the client has paid for an hour of sex he is owed an hour of sex. Once that hour is over he is owed shit.
Clients don't pay for an hour of sex, they pay for an hour of my time. If they want to fuck something for an hour, I suggest a flesh light as they have no consideration for the human on the other side.
The provider shouldn't kick the other client out, but until you have to deal with being in a vulnerable position with a man stronger than you saying "I'm almost there, I'm almost there" you wouldn't understand the position we put ourselves in by starting another round we can't finish. I'm not saying kick him out when he's done, but if there isn't enough time, it's not happening, I'm not increasing my risk because you want to "get the most" for your money as if I'm a buffet or something.