I wouldn't worry about time at all, I think if it is right someday, you will probably know it. My ex husband and I broke up due to major agreement breaking, and although we did try to date after we broke up, it didn't work out because of course, he hadn't done the work to figure his shit out.
We stayed friends though, he saw a counselor for a bit, and did get more introspective and work on his issues - I'd say it was about 5 years before he got himself together enough that he wasn't making damaging mistakes in relationships he was in, and he crushed a few people's hearts during that time of growth, I think he's been making much better decisions for the last three years or so, while avoiding hurting people. Dating wasn't on the table for us again, but I just wanted to give you one example of how long things can take to change. I think regular therapy would've sped that up somewhat for him though.
I guess my advice is...don't wait, be friends if you enjoy each others friendship. if someday you think dating would be healthy for both of you and you both still want it, that's when I'd give it another chance.
Happiness will never come to those who fail to appreciate what they already have.