I let them and their shape dictate to me. Most pups will stop one of the feeds on their own but some dogs are just greedy. Must say, I keep the 3 feeds a day till about 9 months if I can(not had many that eat so often for long) for large breeds and 6 months for small breeds.
My dane pitt dropped the 3rd meal at about 6 months- she just wasn't showing interest in it. Also realized my measuring scoop was off and I was giving a lil more then I intended and started using my measuring cup. Stupid me! Now she is on 2 cups a day at 7 months and eats great!