Hiding away, WWM, is quite normal, especially for female cats, the boys tend to be more confident.
They come out when ready, as lots of comments have said. Our first cat was a Tortie, very small - and very clever. She had lots of hidey holes, used to like cardboard boxes to sleep in (we brought them back from s'markets) until after about a week they smelled of cat, and were abandoned. Another fav spot was on the chairs tucked under the dining table, just enough room to snooze between the chair seat, and the underneath of the table.
One day - she'd been with us for a couple of years - she completely disappeared, not a sign. We scoured the house, calling, nothing. After several hours, I looked up in the kitchen, there was an eyeball peering down at me from the top of the high level kitchen cupboards. Once discovered, she never went up there again. In the summer, she'd be off down the garden for most of the day.
One point - do you talk to your cats? May help them settle in, feeling that they're being included? And of course, they pick up on key words. The tortie got to know what "vet" meant, and became uncatchable, so we had to find another term!