Helen, it depends on the manufacturer of the vaccine which your vet used.
If you know the name of it, you can look it up on line and it should say how long to wait.
Duramune is 2 weeks from the 2nd vaccination.
However, it's also worth saying that firstly most pups are covered by the 1st vaccination - the 2nd vaccination is only there to make extra sure.
And secondly, there are many people, myself included, who think that the benefits of early socialisation far outweigh the tiny risk of exposure to disease. I know of people who take their pups out and about everywhere, on the ground and meeting other dogs, from the moment they get them home. I myself am a bit more cautious than this - I wait till about a week after the 1st vaccination, then I take them out and about. I live in an urban area and have never had any problems.