31 minutes in episode 1, we see Robert Gant and then Hal Sparks' butts.

7 minutes in episode 2, we see Randy Harrison's butt.
8 and 15 minutes in episode 2, we see the bare butts and penises of some extras.

30 minutes in episode 3, some extras are undressed and we see their butts.
35 minutes in episode 3, we see Randy Harrison's butt.