Not necessarily. I have had stealth breeders, getting the job done seemingly within half an hour or so, and have heard from other folks whose males are also quick operators.
Seeing a hemipenal cast just means that a hemipene was out. That's it. They're not needed for breeding and they are not a true sperm plug, as seen in other species. They're just an icky booger of sloughed skin, dry/dead semen, and snaky secretions.