AF due today , rise in BBT

Hi ! I have been charting regularly over last couple of months, my luteal phase is 14days consistently. I usually get dips in bbt starting from 12 dpo to 14dpo followed by AF. I got a dip in bbt below coverline yest (14 dpo) so I was sure that i am out for the cycle and was expecting AF to show up anytime. I am 15dpo today and had a super high rise in bbt-much higher than I have ever had before so i excitedly took an hpt but BFN :( Ideally when should I test after rise in temp ?