Heres a tile roof we cleaned yesterday in The Woodlands, TX. This was the biggest one we did this week and it took about 4-5 hours. We also did the driveway which was HUGE.
If you think roof pressure washing is a good idea, think again. High pressure can cause tiles to break, force water under the tiles, strip the color from the tile roof, etc...
A low pressure chemical treatment is what is safe and recommended.