does ovulation occur around the same time every month?

yesterday I used an opk for the first time and it was positive. so I assume that means I'll probably be ovulating today. I bd twice yesterday once in the morning once at night. the last couple months I've only been bd mostly during what my apps say is my fertile week and haven't gotten pregnant. but since that positive opk I guess I'm ovulating about 5 days earlier than expected. which now makes a lot of sense. I'm feeling really good about this month now that I'm about 90% positive I caught that egg :P

so does this mean I've been ovulating about cd 9/10 every month? or is it possible to just ovulate early once in a while?