I don't know; it FELT like about two hours. My perception of dream time is always really off, so i'm not exactly sure. But I remember going and doing all these long, time-consuming things during the dream.

I think i may have actually taken two REM cycles though because I almost woke up and one point, probably after about 90 min. so that's my theory.

Either way, I experienced it as about 2 hours.