How much canned food should I feed my cat?

The more I read here and other places everyone says to switch to 100% wet food. How do I know that the cats are getting enough food? I dont know if I like the idea of them only being able to eat when we feed them and never any other time. We work crazy hours (out of the house by 6AM and not back until 7-8PM) and... show more The more I read here and other places everyone says to switch to 100% wet food. How do I know that the cats are getting enough food? I dont know if I like the idea of them only being able to eat when we feed them and never any other time. We work crazy hours (out of the house by 6AM and not back until 7-8PM) and we are out of town nearly every weekend. How do you do it?
Update: One of the cats has had urinary tract problems twice now, so this is why I want to switch to wet food.
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