Interesting. What I am going to say may not pertain to us. First, those I know with one ovary have regular periods.

Second, my college friend had her right ovary and fallopian tube and 2/3 of her left ovary removed. Her cyles were regular. Interesting.

I can't exactly answer your question but I'll weigh in with my experience for what it's worth 😊
I lost my left ovary to a giant endometrioma (doctor said there was no ovarian tissue left to save when she was in there during surgery). I got a Mirena IUD placed a couple months after in 2019 and that has stopped my bleeding so I have no idea if my very irregular cycle is any better or worse now. I also struggle with PCOS and I guess I mostly blame that for my irregular periods, I now suspect endo was to blame for why they were sooo heavy and painful. Whether it's from getting the endometrioma removed or the birth control or the combination, I don't have the PMS type symptoms I used to so intensely now, which is a relief.

I know that the menstrual cycle is supposed to be regular after a period of time, when the body can regulate the cycle with the pituitary gland and rely on one ovary, but I want to know how long the body needs for the menstrual cycle to be regular after one of the ovaries stops working, how many months or how many years?

It is strange that you suffer from polycystic ovary syndrome. In addition to stage 4 endometriosis. Although most studies rule out the occurrence of both conditions at the same time. 🥺Anyway, I took Visanne for a year after removing giant chocolate cysts from both ovaries. After stopping the medication, I discovered that the left ovary had stopped working and only the right ovary remained, and my menstrual cycle is now completely irregular.