Young rabbits can have pellets available all day long. However, if your rabbit has not been eating any, then it is a good idea to introduce them slowly. Likely he will devour them which is why it's a good idea to start slowly so they don't shock his system.
Also, once he gets used to the pellets, monitor his hay eating. If he eats less hay in favor of the pellets, then the pellets will need to be reduced. We want him eating lots of hay.
As for veggies, think more in terms of "greens" than "veggies." Those can be slowly introduced at around 12 weeks of age. Here is a guide for how to introduce them safely:
Needs alfalfa til 6 months--extra calcium and protein, then wean over to regular hay. Our full grown rabbits get a tablespoon of pellets 2 times a day--when they were babies(up to 6 months)they got unlimited pellets. Some of ours would eat nothing but pellets and others not so much, so you can vary it depending on the bunny--our avatar would get a small dish full and they would last her more than a week--she really liked hay more.