got a foster kitty. need advice!

I just brought home Timmy, a one year old male tabby from the shelter. He is the second foster I have ever had. He's getting over a URI and is kind of lethargic but shelter vet saw him earlier and all well. I put him in his own room with water, food etc. He is hiding in the closet for 6 hours now. Not drinking or eating.
My own 2 cats never hid when they came home. In 2 hours they were fine. My last foster, just walked over and started eating and playing right away.
How long should I let this kitty hide in the closet before I get concerned? Can I leave him overnight?
Thanks for advice, all experienced cat folk!

I think it's OK to leave him overnight. It worries me that he's lethargic and not even drinking though. If there is no change by this time tomorow, I'd recommend you take him back to see the vet.

Also please know that URI's are very contageous and you can spread it to your own cats on your hands or clothes. If you can, use a different set of clothes when you're in the room with Timmy and of course, wash your hands and forearms well after every visit with him. Has he been tested for the major feline illnesses?

Yes, the drinking part worries me the most.
I've been instructed about isolating the URI cat, and washing hands and dishes thouroughly. Didnt know about changing clothes. I guess I will wear a smock when Im in there.
Timmy has gotten his shots in the last week. The only other problem he has is some ear mites. I can deal with that.
Ill check in with him later to see if he's been out of the hiding place. Its just so sad to see him back of the closet among the shoes!
I'll post again tomorrow to let you know.

I can't advise about the eating and drinking but we have had cats that hide for days after coming to a new place while drinking and eating little. I think it just depends on the cat's personality and their life experience. Poor guy. Hope he comes around soon!

Mornin'
Happy to report that Timmy drank and used his box last night. He left the closet and now behind the linen shelf. I guess I can let him alone for the next few hours.
The next challenge is to find a food he likes. He is very skinny and Id like to get a pound or 2 on him.

I have 6 cats, and 5 of them acted like they had lived here all their lives when I brought them home. The other one, Henry, his for 6 months. He would come out when I wanted him to snuggle, or to eat and potty, then would go back up to the top of his kitty condo. Some cats are just like that. Yours will come around eventually. It sounds like he already has a little bit.

If you're fostering regularly, you probably know about KMR -- Kitten Milk Replacer. We always gave it to our fosters who needed to plump up!

This is one finicky boy. He doesnt want anything else but dry food. He is eating some Science Diet and Purina Natural. All the tempting canned foods he ignores. But he is getting enough water and eating more than yesterday. He came out of hiding in response to a toy today. Definitely less worrisome.