First Week

The first week decides how the next ten years feel. International Cat Care's settle-in guidance is specific about the mechanics: start a kitten in a quiet room for the first few weeks, keep an adult cat indoors for at least two to three weeks before any outdoor access, and set the room up properly — litter tray in a discreet corner, food bowl on the opposite side of the room, and the water bowl a few feet from the food but well away from the litter. Cats like to drink after eating, so water near the food is fine; water next to the litter is not.

Use familiarity as a tool. The same food, the same litter and, if possible, a piece of bedding from the previous home are the three cheapest ways to make a strange room less strange, and pheromone diffusers can help some cats settle. If the cat hides, resist the urge to pull it out: spend time in the room at floor level and let the cat close the distance. A cat that only eats and toilets overnight in the first days is normal; a cat that is still not eating beyond that needs a vet call.

See the first 72 hours plan, helping a shy cat settle and why cats hide after adoption.

Source: International Cat Care — Helping your new cat or kitten settle in.