Positive opk

So I had. A positive opk this morning at around 5am. BDed last night at around 7 and plan on doing so tonight at bedtime. Well I took another opk right now (9:21pm) and it's negative. Is this normal. I've never really tracked my ovulation by taking OPKs before so I'm not sure what the norm is. Is what we did last night enough for my surge or will BD tonight with pre-seed even be helpful???