We have a border terrier, Gylly, who is now 8 months. So this is a recent memory for us!
It took Gylly to to three months to stop weeing inside. No. 2 was a lot quicker than that to get sorted. As soon as he did a pee, we would pick him up and take him outside, that is all we did really. If he did a wee on the newspaper [by the door] he would get a treat and a ‘good boy’.
It may be that some dogs learn quicker? According to the lady who runs the puppy training classes we attend, it can take 2-3 months for their ‘bladder control muscles’ to work well enough to hold it in!
1 recommendation from a friend of mine was to go outside and pee in the garden yourself! The dog will copy, thinking it is the right thing to do…..