Generally, I prefer to free feed my torts, or allow them to free graze on their own, and make sure growing conditions are correct for that species, age and size.
Hatchlings should be able to eat when ever they want. If he eats it all, give him some more. Then the next time you feed him, give him a little more then you did the day before. I always liked my leopard to have some left over the next day. A waist yes, but I knew he had enough too eat.