Our box turtle in winter goes as long as several months w/o eating. In fact some years it hibernates from a few weeks to a couple of months. This is inside at room temperature. During the active months it usually wants to eat turtle food every 2 or 3 days, and it will not touch food unless it is hungry. Ah, so here I have to admit that I let it train me to add a little water to the dry food, and the turtle hates dirty food, so I just have to give it new food when it's hungry. It is always hungry for crickets, roaches, grubs, big grasshoppers, earthworms, big green hornworm caterpillars[1], etc., but those are a lot of trouble to maintain a constant supply.
The turtle's terrarium (a big aquarium tank) is parallel to my path to the office, so I also know it's hungry, aside from the banging, when it sees me coming and races me the length of the tank. Did I mention that it appears to differentiate between me and other people?
[1] A favorite story I like to retell (and Grandpa starts in with...) is when our daughter was oh 11ish and we had a bunch of her classmates over I liked to drop a big tomato hornworm into the turtle tank with the kids all gathered round. When the cabal got packed in tight and a bunch of eeewwws! started I knew that once again, it was nature, green in tooth and claw.