Side-ring EXTRA · Timing of return
Rashi on Vayikra 14:43 (citing Sifra).
English: “If the affliction returns…” — one might think that if it returned that same day it is impure; Scripture teaches [from the parallel] “and the kohen shall return” / “if it returns” — just as the return stated later is at the end of a week, so the return stated here is at the end of a week.
Week-end inspection only
Chazal (via Rashi/Sifra) require that a returning house-nega be assessed at the end of the week, not on the day it reappears.