I started the day my period started. Usually 97.7 or lower pre-ovulation and over 97.7 after your ovulate. 

I would start first day of period (you could start now if you want just might not make much sense until you've done a whole cycle but might just get you used to doing it!) you need to try and take it same time each day as soon as you wake up, before you even lift your head off the pillow! Good luck!

Actually on CD 1 (start of your period)... I started tracking mine and started tracking during my cycle... Opps

I started after my period ended, but I only tracked mine for a couple weeks (from period to BFP) and it happened to be the month I conceived. But I think they say to track it a full cycle so you know when you peak, idk if it matters when you start..