Whenever they poop or look skinny. A regimented schedule isn't good for ANY animal. Sometimes your carpet will spend an extra day or few hours on the hot spot. What does that mean? It means that it will metabolize/break-down its food that much faster. But sometimes your carpet will hide on the cool end an it may take 2-3 weeks to fully digest its food and look normal. Point is, LOOK at your animal and don't follow any of the old "rules"! They're great for beginners who have no idea, but you can simply observe your snake and feed accordingly. Do YOU eat the same thing, at the same time, and the same amount every day forever? Nope, so don't expect your snake to. For example, I looked up a feeding record for a female Jungle I have. Here it is:
July 12: 1 large rat.
July 14: 1 large rat.
July 18: pooped.
July 20: 2 large rats.
Aug. 8: pooped.
So you see, those rules mean squat here. From July 20-Aug. 8, she took forever to digest her food. So I let her. She had access to the same temps and everything else. It just took longer.
The only bad thing with Carpets, is that they are ALWAYS hungry, ha ha!! Good luck man, and watch your snakes!!