Skip the step of etching primer. Just apply a coat of Epoxy Primer, then apply a 2 or 3 coats of 2K High Fill primer.
The etching primer is a waste of time. After sanding or sand blasting the panels, you will have a surface ready for epoxy. Apply the 2k right away. That way you won't have to sand the whole thing down again before applying the 2K later.
If you apply the epoxy or etching primer, and you wait past the recoat window, you will have to sand the epoxy primer first and then apply the 2K primer. So why sand it twice? Put the 2K on as soon as the tech sheet says you can.
Frank