To which certification are you referring? AFAA?
I have a 200 hour certification, and that was one weekend a month (20 hours) for 10 months, with a dozen books and about 200 hours of homework on top of the in-class time.
There’s a lot more to yoga than the poses. But if you are looking for a gym certification, my guess is that you could pass without too much effort. I have three 16-hour certifications to teach gym yoga classes, which is more like a glorified stretch class without the yoga theory or really going deeply into the muscular actions or fascial lines in each pose.