At this age he should be on three meals a day and not down to two until he is about six months old. This age is the fastest growth for a pup and good nutrition is a must as well as enough food to manage growing systems. I have worked and lived with labs as a volunteer with a service dog group. Feed the pup three meals a day. Feed him in his crate and leave the food with him for 15 – 30 minutes. What is not eaten gets picked up for the next meal. Leaving food down all day combined with too much food can lead to obesity in dogs. Leaving food down all day can make it tough to monitor how much the dog is eating which can be vital in helping determin if there are any health issues cropping up. At about five months of age start to reduce the amount of food at his midday meal and increase breakfast and dinner (it is healther for dogs to get two meals a day as it may help reduce the risk of bloat). By six months of age, your lab should be on two meals a day. Again, do not leave food down all day and if the dog walks away from his meal without finishing it, pick it up. A healthy dog will not starve himself but may learn how to use food to manipulate owners.