I do the disc change routine. Watch the time, when a good break comes anytime after say 50 minutes (or maybe even earlier) change then. I usually watch for one of the musicians to look to be changing instruments, the guitarist usually. If he's getting set to change, there will usually be a few minutes when they check the tuning. Or, if there's a gear breakdown problem, etc. I've only had this not work just a couple of times.