hairs have very little to do with it.... the trichs are where it's at. some strains' hairs turn before the bud is ready, some a little after. each strain is different, the only way to really tell when your bud is ready is by the trich color.
then you still got some time...... I'd check them every day or two, see where they are. I usually start flushing when I see that there aren't very many clear trichs anymore. I like a soaring high rather than the couchlock though.