Shocked CD11 positive opk

Jo • Both 41...TTC for too long
I usually (lately) get my positive opk days 12,13 O on 14. Last mo was 13,14 Oed on cd15. Only difference I took it later (6ish pm) in day today instead of 11:30am... Think I caught the very beginning of my surge? Yesterday I took it around 230pm negative. 
​Now we BDed every other day (starting odd cd7)  should we bd again next 3 nights? Like the SMEP plan? Or stick to every other day? No sperm issues.  Btw I'm 40 and this is cycle 10.