Best time to start tracking BBT?

Shyanne • ~TTC #1 since December 2013~ January 17, 2015 we found out we`re expecting!(: our LO was born 9/11/15 @6:01p.m.
I've been wanting to start for some time now but I thought it be better if I waited till CD1. Will it help at all with doing that or will it not matter?