Do you only ovulate after the lh surge goes back to being negative? In other words, can you ovulate and still show an lh surge for several hours?

I posted on another post that my first smiley on the pink/regular clear blue digital occurred at 11pm on CD15 and it was still a smiley in first morning urine on CD17. A test a few hours later on both cheapies and clearblue digital showed negative/empty circle. Does this mean there is no way I ovulated on CD16? I was feeling lower abdominal cramps that day and was assuming I was about to or had already ovulated.