TT #104 · Parshas Tazria · Aliyah 2 · Passuk 7
English: However, if the mispachath spreads on the skin after it has been shown to the kohen for its purification, it shall be shown to the kohen a second time.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:7
Torah Temimah cites Sifra (Toras Kohanim) for when the kohen resumes examination for the transition from impurity to purification.
Sifra — Vayikra 13, Midrash Sefer
English: “For his purification”—one might think the priest must attend continuously while the lesion keeps spreading. Scripture says “for his purification”: he attends when he sees the person moving from impurity toward purification.
Textual derivation
The kohen’s renewed examination is tied to the person’s transition from impurity toward purification, rather than continuous monitoring of every change while the lesion is spreading.