From Dr. Lisa A. Pierson's web site (http://www.catinfo.org/#My_cats_are_now_eating):
This is much longer than the manufacturers recommend leaving their food out. What does everyone think about this? Getting my monsters to eat more wet would be much simpler if I felt comfortable leaving it out longer.An added note about leaving canned food out: Keep in mind that a cat's gastrointestinal tract is much different from ours. I routinely leave canned food out for up to 12 hours at a time for my foster cats and kittens. I have been doing this for many years and hundreds of cats and kittens have passed through my foster room without experiencing any problems from this practice. If the weather is extra warm, I will try to visit my foster room a bit more often but if my schedule does not permit it, then I still do not worry about leaving the canned food out.