opk and surge help

Stephanie
So confused. Last month I had semi positive strips leading up to a high day and peak and slowly back down. I normally test in the afternoon. Clear blue had been low every day. This morning I did a strip (not quite positive) and a clear blue and I got peak completely missing the high. This afternoon my opk are completely negative (not shown) 
Do LH surge length fluctuate like this one month be way longer than another? The bottom 2 tests were this morning. Should I still BD tonight or has the time passed?