We do about five minutes of stretches and between five and fifteen minutes of drills and ukemi practice. At beginners' classes the instructors always say that this is not enough warmup and people should stretch before class. I usually stretch my feet, which otherwise cramp up.
Some of the senior people feel free to skip warmups. As a very junior student I wouldn't do this, but I also know from painful experience that if I don't warm up, I'll hurt myself. I don't know if it's the physical stretching or the mental centering or both.
Our full set of hitori waza is too many for an hour-long class unless they are taken at high speed; we usually do eight to ten of the twenty.
I was a guest at a dojo with a much more physical and high-energy style. They did far more warm-ups and stretches, and took them much faster. I wondered why, till we got to the techniques....