I asked the person at AOS when I bought some of their preshave oil and they said to leave it on for 5 minutes and then lather.
When I use it, I usually put it on after I shower, wash my hands, strop, make my lather, lather up, and shave. I figure that is long enough to let it soften the hair.

A little bit of that stuff goes a long way and it is definitely gooey and slick.