If you had slightly lower temps, they can hatch as late as day 25+. I have had chicks hatch 2 days apart from the same incubator! How is he doing? I have heard some babies can take 36 hours to hatch! I havent been able to let em go 15 hours without going crazy and feeling helpless. Patience is a virtue, but can make you so self blaming in the incubator/hatch waiting game.