Most epoxies have a no-sand recoat window of 2/3 days, some up to 7 days. You can apply filler or primer over it without sanding within that window. After that they usually want you to sand and shoot another coat of epoxy before spraying other products.
SPI has a great paint step guide on their website.
https://www.southernpolyurethanes.com/perfect-paint-job