Yeh with vinyl ester I don't think you'll have much issue with laying up the backing coats shortly after it has cured hard. Technically it will continue to shrink until it is fully cured, and because the tooling resin is a different chemical it will shrink at different rates which theoretically can lead to distortion. However in reality they are both very low shrink resins, and I've never had an issue with laying up within a few hours.