Takes me about 30+ minutes to clay my cars...
Easily 1-2 hours on other people's cars.... Usually the worst part of a detail for me.
Maybe I'm working too hard at this?
I'm in the same boat as you. I just clayed my wifes windshield, and that took 10 minutes. If I extrapolate for the whole car being as dirty as the windshield was, were easily talking 1-2 hours.