My Yorkie is almost 8 months old and I just noticed last week that he hasn't had an oopsie recently! He was 5 1/2 months old when I got him so I guess it took 2 months.
I took him out a lot in the beginning but I noticed he wouldn't go when I was out there -- he wanted to play! So I'd take him outside, place him in the same spot and say Go Potty and then go back in and watch from the window. If he didn't go in about 10 minutes, I'd let him back in and try again in a little bit. If he did go, I'd go out and praise him to high heaven. If I caught him in the act inside, I'd say a dramatic OH NO! and scoop him up and take him outside.
I also kept a puppy pad right next to the door for the times when he had to go but I didn't let him out in time. At first, I'd wipe up a little wee with the puppy pad and put it back next to the door so it had his scent and he made the connection. He got the idea really quickly. As he developed more control and I got to know his habits, he didn't need the puppy pad anymore.
It REALLY helps if you have another dog, though. Bobby watched the others troop out, do their business and come back in and it helped him make the connection. Keep playtime really separate, if you can. When I go outside with them, they know it's playtime.
Good luck!
Julie |