Starting OPK right after AF?

T.
It's my 2nd cycle after BC but technically, since my first cycle was a learning process in DPOs, OPKs and all that this will be the true 1st month of TTC. 
SO is it ok to start charting and testing right after AF? I was on BC for so long that I'm just want to make sure I see the entire picture and not miss a +day.