I would give it a few days to a week, and then try a live hopper mouse. If he takes that, give him another 4-5 days later. Keep that up for a little while, then try to transition him to f/t. Once hatchlings get eating, they seem to be happy eating pretty much anything. That would also be a good time to switch to rats if you plan to. Just substitute f/t mice for f/t rat pups. If he hesitates with the rat pup, you can scent it with mouse bedding...