Ovulated late?

Krystal • TTC since February 2014. Miscarriage at 7 weeks on Dec 4 2015, 2009 son, 2018 daughter
So, normally I o on CD 14/15. This cycle I didn't get a pos opk until CD 19. I've heard that the time between o and af is always the same, is this true? So if I o'd late, af will be late?