I usually try to avoid missing any part of any show for a bathroom break if If can help it, but sometimes nature calls...And it's usually a mad rush for the can at halftime or at the end, so that isn't always the greatest time to go, either...
On the Vapor Trails tour back in Nov. 2002 I went to the concert not knowing the set list. I made it well into the second set but got to the point where I just had to go. It was during the drum solo that I decided "screw it, I have to go, no matter what song is next..." As I headed towards the john, the drum solo ended and they started playing "Resist" (acoustic), and I was quite happy at my timing...So I get to the can, and as I'm taking care of business I overhear two guys complaining about how "Rush doesn't play any of their old stuff anymore, blah, blah.."...As I left they were hanging around, still complaining, and as I get back in and heading back to my seat Resist ends, the lights go black, and I hear the intro of 2112. Perfect
Saw them twice on the S&A tour and had great bladder timing - didn't miss one minute of either show.
At the Time Machine Tour show last year, I knew the set list going in. It was at the MN State Fair and I got there a couple of hours before the show to partake in some of the State Fair eats and stuff and so I pretty much knew I'd have to take a break or two at some point. Since I knew the set list I kind of planned the best spots to go. I'm not a big fan of most of the S&A stuff, so I went right after LTTA during Faithless to beat the halftime crowd and hopefully make it through to the end of the show (I really didn't want to miss any of the 2nd set) , but I ended up having to go again so I went right after 2112, during Far Cry. Got back to my seat with plenty of time to spare and thoroughly enjoy La Villa Strangiato and the end of the show with an empty bladder