Around a year old, which is about the the age that I switch from puppy food to adult. I believe Purina has done some fairly extensive studies on feeding and there seems to be some real benefits to feeding once a day in the evening, giving the dog a certain amount of time to digest the food so they get the most out of it the next training day. You might find the exact info if you go to their web site.
Feeding Schedule
At what point do you switch a pup from two feedings a day to one? I have no clue! Help would be appreciated! 
