OPK on CD 18...still faint lines?

Ka
My main question is this...how long can it take to go from getting faint test lines on OPKs to Ovulation? Glow (which I know is only accurate so often with these things!) predicts ovulation occurring in 2 days! 
Could that still happen? I've been waiting and testing (chronic tester, here!) and this is the darkest my lines have gotten so far.
Any insight would be greatly appreciated! 😊