Kittens Trouble Urinating after Spay

Hello! We just got our kittens spayed on Wednesday. Since then, when one of them eyes to the litter box they squat sometimes for over 40 seconds and only a few drops come out. We took them back in the next day and the vet said their bladder didn't feel full and it's possible they were sore after being expressed before surgery. But it's now been 2 full days since we've seen either of our kittens pee regularly. They have water (but are not drinking) are eating (weve been adding extra water to food), both have pooped, but are not urinating. The vet clinic is closed until after 4th of July. Any thoughts/suggestions? Is this normal or urgent?

Hello!  Cystitis presents like this and can frequently follow stressful episodes (and this is no slight on you or your vet; however well it is handled, going to the vets and having an operation is a stressful episode for a kitten).  These signs are therefore  definitely worth paying attention to.  For a short time after a Spey, small cats can be lacking in body fluid and therefore less likely to urinate out (dehydration).   Kidney problems are a much less common possibility.  It is worth speaking to your vet as they may well offer to check a urine sample to rule cystitis out and check the kidneys' concentrating ability / rule out diabetes etc.   Best of luck, and we look forward to hearing how you get on if you feel like letting us know.