John Gill Commentary Leviticus 13:27

"and the priest shall look upon him the seventh day: if it spread abroad in the skin, then the priest shall pronounce him unclean: it is the plague of leprosy." — Leviticus 13:27 (ASV)

And the priest shall look upon him the seventh day
When that is come, any time on that day; not needing to wait until the end of it, or till, the seven days are precisely up; the same is to be understood in all places in this chapter where the like is used: [and] if it be spread much abroad in the skin ;
in the space of seven days: then the priest shall pronounce him unclean; it [is] the plague of
leprosy :
according to the law; so that it was necessary, in such a case for him to conform to it in order to his cleansing.