Quick Answer. Typically, a coat of polyurethane dries within 24 hours. For example, if polyurethane is applied to hard wood flooring, it is okay for a person to walk on the floor at the 24-hour mark. Oftentimes, a professional places three coats of polyurethane on a hard wood floor. In such cases, 24 hours elapses from the application of one coat to the next. The floor is able to be walked upon at the expiration of 24 hours from the application of the final coat. Provided an appropriate drying period is allowed between coats of polyurethane, the final coat typically dries within a 24-hour time period.