I have MC'd in band battles in Rock venues, and have been quite happy to take a very interventionist approach. If a band has been allotted fifteen minutes, and that has been used up by two songs, I have had no inhibitions in walking onto the stage and interrupting the announcement of a third song to announce that the audience will be able to hear that one on another date, because the next band due onstage is made up of people who are much bigger and more violent.
This approach works irrespective of the fact that it may be a tiny solo performer coming on next. The usual response from the audience was wild applause and laughter.
When I'd done that a couple of times, other bands kept very much to time.
People only keep to the rules when they know that they will be applied.
Would I have stopped someone who started on "Desolation Row"?- yes, with a joke, and a question about which song they were really going to play- since everyone knows that DR was excluded.
Cheers
Dave