Parashas Kedoshim · Passuk 19:06
Chabad.org — English translation + Rashi
Torah Temimah · Zevachim 56b.
English: Might they be eaten on the eve of the third day? Scripture says “what remains until the third day” — while it is still day it is eaten; it is not eaten on the night of the third.
Time limit of two-day shelamim
Shelamim that may be eaten for two days expire at the end of the second day; the night that begins the third day is already beyond the permitted time.