I would say just less than 3 months. DD was fully trained in early January in the sense that she could say when she needed to go and we weren't having accidents anymore (age 27 months). This part was over and done with very quickly - took about two days for daytime training, and then only another couple of weeks for night training.
But it's taken until just within the last couple of weeks (30 months) where she actually goes by herself. Well, she goes at daycare by herself where they have small toilets so she can manage more easily. At home, she will go use the potty by herself (so then I just need to go along after her to empty it) but she can't use the toilet herself because she can't physically get onto it, even with a step stool. She does try to be independent as far as possible, and even when I have to help her get onto the toilet, I usually get "mummy, go away!" as soon as she is on!