Percy Jackson and friends run into the lair of Medusa which is a greenhouse garden filled with statues. A middle aged woman turns to stone after Medusa convinces her to take a peek. The transformation spreads like a wave starting from the eyes but spreads unevenly over the body. Although Percy and his friends manage to defeat Medusa, the woman remains petrified along with the rest of Medusa's victims.
https://www.youtube.com/watch?v=OVOp2jRboBs (Not exact petrification time)