We personally feed our cats and kittens both wet (canned food) and free feed dry kibble. We give wet food in the morning and evening. Ideally kittens would get a midday portion of wet food (if possible), since they are growing rapidly.
Why Feed Wet Food?
First, your modern house cat evolved from desert cats, and this has left them with a low-level thirst drive. Even if your cat is very thirsty, they'll probably never gorge themselves at a bowl of water like a dog might. Another reason hydration is so important in your cat's diet? Your domestic feline isn’t hunting high-moisture prey like their ancestors did. So, for many cats, it's important that they get some of that necessary moisture from their diet—and of course, dry cat food doesn’t have it. The benefits of feline hydration are crucial to your cat’s vitality and wellbeing. Water is essential for helping your cat’s kidneys clean out impurities. Without enough water, that process can break down, possibly leading to bacterial infections and the formation of crystals in the urine, which, if left untreated, can prove fatal. Wet food is great for all cats but is especially great for male cats due to their increased risk of developing a urinary obstruction. Obstructions are incredibly painful, and extremely life-threatening if not taken care of immediately, so any steps that you can take to prevent it from happening in the first place — like giving your cat wet food — is highly recommended. Instead of using wet food as a "treat" or as a supplement to your cat's dry food, it should really be the other way around.
How Long Can You Leave Wet Food Out?
Once opened, canned food has a shelf-life of 24 hours and must be stored in the refrigerator. If your cat does not finish their wet food, it should be properly stored in the refrigerator or discarded. Leaving canned food out for longer than a few hours can run the risk of contamination and cause gastrointestinal upset. The reality is, it'll probably be left out longer than that. It depends a lot on the heat and humidity in your home, but 4-5 hours left out would be ok. Depending on your home setup, and the amount of time you'll be away from home, you may even want to try freezing your cat’s food and leaving it out so that by the time they're ready to eat it, it will have thawed out.