Hm, good question. I’m a bit biased now cos I read an interview with one of the producers of Friends who explained everything about Mondler.
So yeah, I think it was a pretty good time to have them be together. It should not have been done later, but perhaps they could have done it earlier. Again, I read that they did actually plan to do it earlier, but waited because the whole Ross/Rachel drama was still going on and it would’ve been too much with the focus on 2 couples. That’s why they waited. You can see they sort of experimented with Mondler in the S3 finale. And I kind of agree with the way they did it in the end. :)