Adopted Kitten Hasn't Ate or Used Litter in 24hrs

Hey y'all, I'm a first-time cat owner, and only really have experience caring for dogs, so I feel a little out of my depth and would appreciate any advice. I brought home a four month old kitten (from a relative who had a litter of three kittens), and the little guy seems very, very frightened.

He had a 3.5 hr drive home in his crate; he yowled the first hour and seemed to calm down, even dozed off, for the rest of his ride.

When we got home, I neglected to put him in a smaller room to start and instead put him in the living room. I think he was very, very overwhelmed. He slicked around for a few minutes before darting under the couch, and he's been there since last night crying off and on. I heard him moving around last night, and he even jumped up onto my bed before I scared him off, but he never touched his food or litter.

He's moved even less today, but he's quieted down. I haven't tried to touch him at all, but I've been sitting on the couch reading/watching tv and puttering around in the living room. I want him to be familiar with me, but I'm afraid I'm scaring him.

If he doesn't eat/use the bathroom overnight should I call a vet? How normal is it for a skittish cat to not eat or use the bathroom?