There aren't any hard and fast rules, so far as I'm aware. StackExchange is kind of making things up as they go when it comes to graduation. Which is fair, since this is kind of a new thing in general.
The primary indicator for graduation at this time is site growth. When you plot the views per day against time, they want the graph to be increasing dramatically as it moves to the right.
We don't have that at this time. Our views are healthy, but they tend to be stable for a long period, followed by a spurt of growth, followed by a new (higher) plateau. We have yet to figure out how to achieve the continuous explosive growth required for graduation.