I don't necessarily agree with Bowen's comment about the double-move at 8 yards. Maybe that's how it is in the NFL, I've not watched closely, but the double-move I'm most familiar with is the hitch-and-go, which happens at 5-6 yards. The receiver puts his chest and ass down, and starts a stop break. From there, he can either lean forward again and release outside the corner, who should be in his roll break, or flip his outside shoulder upfield to simulate the hitch (often accompanied by flashing the hands and a pump fake), then baseball-turn outside and head up the sideline.
The quicker double-move is meant to suggest an in cut, and you can have in cuts between 5 and 15. Dig routes are often run at 10 yards. There is not a lot of difference in real time between Bowen's 8 yards and 10 yards, especially since cuts are often close approximations affected by the receiver's speed, his place on the field, whether he was on or off the line, and so forth.
I'm no coach but if I was I don't think I would teach that particular piece of advice.