Plan b on period?

So I just wanted to double check; I’ve looked on Google but it didn’t give a clear answer. Last night when I was w my man, the condom slipped off as he was pulling out to finish, we think it was cuz we kinda messed w it a bit which made it looser, so our faults. But since he finish kinda inside of me (??? not all the way but on the outside more so I still wanted to be safe w it) we went td and got a plan b. If im in the middle of my period would plan b still help in this case? Since usually I don’t ovulate till a couple weeks after. Or was a plan b not necessarily needed since my ovulation wouldn’t be for at least a week / and a half?