TT #94 · Parshas Tazria · Aliyah 1 · Passuk 5
English: On the seventh day the priest shall conduct an examination, and if the affection has remained unchanged in color and the disease has not spread on the skin, the priest shall isolate them for another seven days.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:5
Torah Temimah cites Sifra (Toras Kohanim) for the suitable daylight and clear vision required for examination.
Sifra — Vayikra 13, Midrash Sefer
English: One might think any daytime appearance is suitable. Scripture says “to all the appearance of the priest’s eyes”: just as this excludes a priest whose eyesight has dimmed, so the day excludes times when daylight has dimmed.
Counting rule
The Sifra limits examination to suitable daylight; early or dim light can distort the apparent intensity of the mark.