Positive on CD20. BD on CD 11-CD15. Is it possible to still get pregnant?

I usually have a 28 day cycle. My DH is on travel a lot so it's hard to sync our schedules. He was here and we BD on CD 11, 12, 13, 14, and 15. I have been getting neg OPKs. He had to leave then on CD 20 I received my first pos OPK. Is it possible to still conceive? If not, he will be here on CD 22. Is it possible to hit it then? It seems really late to get a pos opk on CD 20. Any advise?