I have a B17 on my Surly LHT, and am largely quite satisfied with it. I have just short of 800 miles on the saddle, and all of the chafing and numbness that I was experiencing from other saddles is no longer an issue.
When I ride - usually about 30 miles at a time - I pretty much stay on the bike the whole way, and usually take about a 5 or 10 minute break at my turnaround point. This is usually about an hour or so into the ride (depending on the route I take, the wind, etc., I average between 14 or 15 miles per hour).
The only problem from the saddle is a kind of "bruised" feeling - I don't how else to describe it - that starts to set in about 15 miles or so into the ride. I think it's just an issue with how long my weight rests on the hard saddle. It's kind of like when you were a kid and you played that game where another kid would hit you repeatedly on the same spot on your arm, if you know what I mean. But, by the time I get back home I am REALLY ready to GET OFF THE D@MNED BIKE!
I try to take short "coasting breaks" when the opportunity presents itself where I support my weight on my legs off of the saddle, and I shift my position around by riding in the drops once in a while. I am not in the habit of standing to pedal, except in very short bursts to crest a hill, etc. I am currently wearing Performance Century shorts.
I have never ridden as part of a group - I always go solo - so I don't really know how often other riders take breaks. Is an hour or more at a time in the saddle asking too much of my physiology? Should I get off for a minute or two, say, every 30 minutes or so? Any other suggestions?