Its not the sort of thing you need to leave out. They usually finish within mixtures (meaty bones can take longer depending on type). You put out their breakfast before you leave. And then give them dinner when you're home again. Domestic cats are crepuscular so most often hunt and eat at dawn and dusk anyway. Just be aware that meaty bones can be a bit messy so you might want to feed those at a time of day when you can supervise them and train them to stay eating them on a silicone floor mat (and the like) so they don't go running off with their 'prey' lol.