yeah you have one guy hold it upright. Then have two guys, one on each side apply the vinyl at the exact same time.
Regular Method:Better question: why? Do one side, then flip it and do the other. There is no time saver by doing both at the same time, even if it could be done.
10 min. was just a guess, applying it a 4x8 sheet of coroplast might not take that long, all it is is lining up the graphic, tacking one side down, and doing the rest using the big squeegee.