Self Etching primer would be a waste, it's designed to etch metal to anchor itself. You don't have any bare metal.
I'd call Dupont's Tech Service line and ask them.
Checking a few reference sites, it looks like 7 days is the window. Some manufacturers say sand and apply another coat of epoxy, some say scuff and apply a sealer.
If it was my car, I'd scuff it up with a scotchbrite pad and shoot a sealer before base coating it.
