Breaks in raid.

[Meillquei]

My previous raid group had a 10 min. break halfway through.
My current raid group doesn't really have a set break time, because people tend to go afk whenever they need to smoke/bio/whatever. Sometimes there might be a 5 min. break inserted though.

[Halicia]

10 min break timer about 90-120 mins in. (generally around the halfway point for the night).

5min breaks as necessary, but generally having the 'scheduled break' coming up avoids those.