Sex and TTC

Wondering if anyone else's husbands have difficulty finishing during sex. My husband says it has always taken him a long time to finish... We're TTC and have sex 2-4 times per week, sometimes more, but he only finishes occasionally. It doesn't seem to bother him and he's nearly always ready to BD, so it's not an attraction issue. I've heard some medical conditions can cause this, but he's not concerned enough to get checked out...