I've left raw out for several hours without any issues. There does reach a point when the cats decide it's unappetizing, but they've certainly still eaten it well beyond the half hour max that some people adhere to.
My feeding regime is to give 2 raw meals a day, which is typically eaten within the hour (if not all at once), and then to also leave out some canned for free-feeding.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler