How long will canned dog food remain safe for small dogs to eat?

Can I leave an opened can opened all day without it becoming unsafe for our small dog to eat?

An opened can on a warm day will spoil in about an hour. Maybe it's time to switch to leaving out some good dry food.

First of all, dog food of any kind, wet or dry, should never be left out for the dog. Your dog should be given 15 minutes to eat and any left over food should be taken away. The only exception would be at the advice of your vet in conjunction with treatment for a medical condition. Canned food will start to grow bacteria within an hour of having it out. Whether or not this will harm your dog is unclear. Your dog is exposed to more harmful bacteria every time it licks it's butt. So do what you are comfortable with.