It takes as long as it takes, really. Some people wouldn't really consider a dog fully housetrained until it has been reliably clean for a good few months.

I still maintain that the best thing you can do is teach them to wee on command and it's so simple - just watch them like a hawk whenever they are outside, and when they wee, say "weewees" (or whatever) over and over, while they're going. Then you avoid the situation of being outside, fairly sure they need a wee, but them not going, and then possibly making a mistake in the house.

You need to make sure that you are outside, in the right place, EVERY time they need to go. People underestimate just how many times you need to take them out, to start with.

On waking.
After feeding.
After play.
After a drink.
After a training session.
When the adverts are on.

The more times you happen to be in the right place when nature pings that bladder, the quicker they learn