The argument seems to be that if it only takes a short while for the dust to turn red, if the dust is red it must mean it just happened a short while ago. Is that the way you read it? So if it only takes a day for my wall paint to dry, if my paint is dry it means I must have painted yesterday?
Could be, but not necessarily.
You're leaving out important information to make an informed decision.
If your wall is dry but bright and clean and free of marks, that could make it as fresh as yesterday...or somewhat longer. There's just not enough information.
But what if your wall was not only dry but chipping, peeling...and what if part of the wall is so old it's not even there...the wall itself has fallen over...???