Guinea pigs in the wild are most active at dusk and dawn (there's a term for this, but I can never remember what it is) and you may find that this is the case with this little guy as well. However, many are the most active when you are. They will also be periodically active throughout the day and the night. They have to eat at least once every four hours so they will be up and moving around at all times of the day and night as a result.
In other words, you should [*]not[/*] take his food away at night. Guinea pigs are lagomorphs. They have a cecum, which is sometimes called a second stomach by some people. Food always has to be moving through the cecum in order to prevent bloat. Bloat, gastrointestinal status and system shut down result from a lack of constant food intake. The end result is death and it doesn't take long to happen in most guinea pigs, which is one of the reasons I think some of us find it surprising he survived his former living conditions with the woman you got him from.
Your little guy always needs food available. His diet should consist primarily of hay, but you should always make pellets available too, in order to ensure he has access to, and is getting, enough food. If he doesn't eat the hay for some reason, you still know he has pellets he's consuming.
By the way, since he's a baby, he should have alfalfa hay and alfalfa based pellets in order to promote healthy growth. At somewhere between 6 months and 1 year, dependent upon the source, you'd want to switch to Timothy hay, orchard grass, or a similar grass hay, as the primary diet, and timothy hay based pellets. Alfalfa is higher in fat and calcium which help young piggies and pregnant and lactating mothers, but is generally considered to be only appropriate as a treat for teenage and adult piggies.
Pigs are prone to the development of bladder and kidney stones, which is the reason calcium dietary intake is so important to consider. Phosphorus also plays a role. You have to be careful about veggie diet components for the same reason in adult pigs.
If you don't have alfalfa available and only have timothy hay, that's ok. You can choose veggies higher in calcium for the first however many weeks he's with you to help his little body grow.
such a lucky boy to have you- keep posting 