Quoted: 0 Post(s). Duplicolor engine enamel primer...how long to wait. Hey guys. I put the primer coat of Duplicolor engine enamel yesterday and I was wondering when I should put the final coat of color on top of it. Do I need to wait the 7 days for the primer to cure or is it ok to put the color coat on over the primer today and let it all cure for 7 days?