I don't think anybody really knows how long you need to wait before cycling. Everybody is different; their operations are different, their surgeons are different, their exercise history is different. If your surgeon has offered an answer, I would follow their advice.
Otherwise, I would just ease into it gently if you are keen. I started (a lot sooner than anybody on here) by cycling standing up (assuming you have a bike where you can do that easily). Then, I gradually increased the amount of time that I was sitting on the saddle until it felt comfortable again. After that, I just carried on as normal.
Some people will wait six months or longer to give their erectile nerves the best chance of recovery. For me, the health and mental health benefits of cycling as part of my recovery were more important, but you have to make your own decision on that. Two and a half years after my operation, I get erections with and without Viagra, but not as hard or frequent as before. Maybe they would have been harder/more frequent if I have waited six months before cycling. Nobody will ever know, but I am happy with my approach.