How long would it take me in a taxi to get to SFO Friday morning from the Lower Haight?

I have an early flight (well, early for me, its at 8:30) on Friday and trying to maximize sleeping time. I want to get to the airport by 7:30. The shuttles want to pick me up really early, earlier than I would need to leave if I took a bus and BART. How long would a taxi take? Is there traffic in that direction around 7am on a Friday?