I've always read online that the best time to BD is in the morning when you're ovulating. BD every other day before/after you ovulate. You can even wait a couple of days in between. So Monday BD, and then BD again on Thursday. Sperm stays in the females body up to 48 hrs I believe. I think that's what I read on a website a few weeks ago.
However, I think even if you have sex every night... you will eventually get pregnant. One of those spermies will catch the egg.