The recoat time for epoxy is dependent on a number of factors, including the thickness of the epoxy coating and the ambient temperature.
Always follow the epoxy manufacturer's instructions for cure times and recoating. And if you miss the recoat window and the epoxy has cured, follow the directions for removing amine blush, sanding lightly, and removing sanding residue, before applying another coat of epoxy. The reason for sanding cured epoxy is to allow the next coat of epoxy to adhere properly and form a strong mechanical bond.