Unlike a new AVF, a new AVG does not
require smaller needles sizes or slower blood flows, although it cannot hurt. And although a graft does not have to mature, of course, at least 3 weeks should pass before the first cannulation (to help it get "anchored" in the tissue).
So if there are conflicting opinions in your clinic, they may all be right

I would recommend checking your company's P&P, which should specify the initial cannulation of both AVFs and AVGs.
DeLana