The timothy hay is fine. They should have unlimited hay at all times, so if he's eating all his hay and runs out, always give him more. Hay is healthy for them and doesn't make them overweight.
For pellets - what kind are you feeding? Are they made of timothy hay or alfalfa? How much does your rabbit weight?
If you looked at the link I posted, this is what they recommend for a rabbit under a year old.
What quantities of food should I feed young adults? (7 months to 1 year)
introduce timothy hay, grass hay, and oat hays, decrease alfalfa
decrease pellets to 1/2 cup per 6 lbs. body weight
increase daily vegetables gradually
fruit daily ration no more than 1 oz. to 2 oz. per 6 lbs. body weight (because of calories)
But if he's only 5 months old, then this is what's suggested...
7 weeks to 7 months--unlimited pellets, unlimited hay (plus see 12 weeks below)
12 weeks--introduce vegetables (one at a time, quantities under 1/2 oz.)
Since he would still be growing, you don't have to limit food (pellets) as much. Keeping in mind that every rabbit is diffrent, I would consult your vet and see what they recommend for your individual rabbit. But really, at 5 months, you don't usually have to worry about overfeeding as much as you do when they are adults. When he gets to be about 7 months, you can decrease his pellets to the recommended 1/2 cup per 6 lbs. body weight. When he's a year old, the recommended amount is 1/4 cup pellets per 6 lbs, or you can keep him at 1/2 cup if he's really active.
Getting the diet right when they are adults can be more tricky. How much pellets you feed should be based on how much veggies you feed. If you feed them a lot of fresh foods, then you can decrease the amount of pellets.
For now, just make sure that if he's getting a lot of pellets, that he still eats hay too. You don't want them to eat only pellets and leave the hay because that could cause problems with his teeth. If he where just eating the pellets and leaving the hay, that's probably one of the instances when a vet would recommend to limit pellets even though he's still young.