Probably a dumb question, but would it be the week before your period?

I'm on BC (switched from the pill to the patch a month ago) & my husband wears comdoms, we're trying to find out when it would be safest for him to not wear a condom and finish.

I know it's possible to follow your cycle and use that as a way to lessen the possibility of pregnancy, I'm trying to figure out how to do that on top of BC, because we hate condoms.