From that link above....."This is how it works. The next time you're out to
take night photos, go ahead and snap a picture of Scene A, as you normally
would. Then, when it's convenient, take a photo of the exact same Scene A
again, but with the lens cap on."
Why would you have to be in the exact same Scene A again to take a picture
with the lens cap on?
Obviously, you don't.
I think what the OP is trying to say is that using a dark frame
reduction will get rid of any hot or stuck pixels that the long
exposure might make.
However, you obviously don't need to aim the camera at the same scene,
as the lens cap would intrude; just being in the same place will
suffice. Because...
The temp at the time the shot is taken can make a difference.
So, saying "at your convenience" is wrong, too, since, in order to
have the same environmental conditions, the dark frame shot should be
taken immediately.