Ask your vet about feeding them both the prescription food. Pete used to eat the c/d formula. He's switched a different brand now, but all my cats eat it. I tried feeding on a schedule and had a kitty revolt on my hands--which involved large amounts of pee on my kitchen counter! My vet said the prescription urinary tract formulas are safe for any adult cat. I free feed everyone Pete's prescription food and they are much happier with that. When I had a kitten, she got a growth formula until she was about 10 months old.

I give out canned food in the morning. Although it rarely happens, if it's not gone in 30 minutes I empty the dishes.