How long after being spayed will a cat use the litter box?

My kitten was spayed yesterday, and she's home today. She has eaten just a tiny bit, which I'm sure is normal, and not had much water, but she also has not used the litter box yet. I honestly don't know how often she used it before since it's in the basement normally and I just don't pay attention. HOwever, I have a seperate box for her in my bedroom right now where I'm working and keeping an eye on her, and she hasn't used it yet. She's been home since 9:30 a.m., and it's not 3:40. Should I be worried? Other than this she just seems kind of groggy.

I would give her until tomorrow afternoon. Her system was empty before the surgery, and now she's not eating much. Keep an eye on how much she eats and drinks, so that she stays hydrated.