Time is really difficult for me to gauge in lucids, but maybe 10-20 minutes? Depends on what I'm doing. I rarely seem to wake up naturally during a lucid, always seems to happen because I try to do something that ends up collapsing the dream. I write down the times I wake up beside my dream journal notes throughout the night, and based on that, I seem to be becoming lucid at all different points in the cycle, be it 20 minutes after I went back to sleep or an hour.

Which begs the question, if I become lucid early on in the cycle, does that mean that my lucid dreams could run over an hour if I were able to keep stable that long?