i have never done it in sections...you can just lay it down, lace side up and start from back to front...i have never been concerned with timing. reason being, by the time i get to the front more than 3 or 5 mintutes have passed. i cant imgaine how leaving it on longer can be bad, the idea is to dissolve the know. whats going to happen, dissolve the knot to much? lol only thing that can go wrong is if it seeped through, and that would be because you used big dots.
btw you could wait a few more minutes after applying the last dots.
i use one of those thin, pointy artist brushes. you are making small dots.
DO NOT do it again i'd say for at least 3 to 5 days having wet, shook, combed, brushed, wet etc over the course of those days. you should probably do a Got2B attachment so you can see where you are as far as density and hairline, thats really the only way to tell