On the site I'm working on now, the homebuilder gives their guys 15 minutes at 10 a.m., and half an hour at noon. They use two framing subcontactors. Both of them take 45 minutes, one at 11, and the other at 12, but no 15 minute break. The outfit that's doing the sitework works 4 tens, sometimes 5, and like Greg, for lunch they grab something on the go.
About 20 years ago, I worked for a guy who ran his operation the same way, and it got me out of the habit of stopping for any break. I work straight through, although when I start and quit varies with the circumstances. If I'm going to be on the job, I'm not going to waste my time by stopping for some arbitrary number of minutes, just because...