The sooner the better. I would at first cut often just to get them use to having them cut. So many dogs are so hard to handle with nail cutting cause they get away with it in the beginning. Don't let them scare you, cause at first it will be a struggle.
We started Diesel off early and never gave in to his struggles and now we have a more managable dog that I myself can cut his nails.
I think the key to cutting nails is
A) using a good nail cutter, popular brand is large orange handled, I would not use the gilitine(spelling?) kind. They are hard to control when you cut.
Then when you cut cut side to side , not straight across. This way you don't pinch the whole nail and you can cut small pieces easier without cutting to far up and hitting the quick.
Good Luck!
Baking soda is also good if you hit a bleeder.