Many factors are going to affect the timing including where you are staying, where you are having dinner and how you are getting there. If you are staying at the Poly and dinner is at the Poly, then timing can be cut a little closer. If you are staying at Boardwalk and taking Disney transport to dinner at the Poly, then, an hour and a half might not be enough time.
In general, I would agree that the plan should be for a 4.5 hour round, however, we have left the course on a couple of occasions to make dinner resrvations when we were tracking for a 5+ hour round. It can happen.
As to the comment in post #5 about pricing going down after 10AM, that is true up until September 30. October brings a new season for the golf courses and the pricing does not go down until twilight rates take affect sometime around 2 or 3PM. The Vacation Club Golf Membership does give a substantial break after 10AM and there may be other memberships that also give breaks but it is pretty much full price from 7AM until the twilight rates kick in during the October-Dec season.