conception outside of my "best days"

How hard is it to conceive on the days that aren't green on my calendar indicating prime ovulation time? I ask because I don't think I'll be on my "best days" the next time I see my fiancé. We have to take what visit days we can so it's not really possible to plan around ovulation. If Glow is correct (it's been decently accurate so far) I'll see him 2 days AFTER my green ovulation days end. How possible is it that I could get pregnant in those 3.5 days I get to see him? Just curious based on experience from all of you lovey ladies!