I'm sure all performers have experienced this at some stage'

For example, a festival is running a 3 hour session with 6 acts (ie 6 x 30 minutes), and no mc - the acts hand over to each other.

Act 1 turns up when they are due to start, spend 20 minutes setting up, and then play for 30 minutes.

Act 2 then overuns their set by 15 minutes.

By now the event is overrunning by 35 minutes:

What should the other 4 acts do?

Option 1 - each of the other acts cut there sets by 10 minutes (which we did last time this happened)?

Option 2 - cut one of the performers?

I'm sure there are even worse horror stories - not just from the perspective of the performers but also audiences who may have come to see a particular act and were short-changed. I've been to some clubs which had a guest booked, the mc got the 2nd half started off late, spent ages trying to get his huitar ion tune, and finished his spot halfway into the guest's time.

So, another question, what should the proper etiquette be for keeping timings on track?