And the 60th mitzvah is that we are commanded that every animal we sacrifice must be no less than eight days old. This is known as being m'chusar z'man b'gufo (itself lacking time).1

The source of this commandment is G‑d's statement2 (exalted be He), "It must remain with its mother for seven days; then, after the eighth day, it shall be acceptable as a sacrifice." This commandment is repeated in other words in the verse,3 "It shall be with its mother for seven days [; from the eighth day you may offer it to Me]."

This mitzvah covers all sacrifices, with all the various categories of individual and communal offerings.

The expression, "After the eighth day, it shall be acceptable," implies that beforehand it is not acceptable. This clearly indicates a prohibition against bringing the sacrifice before the proper time. But the prohibition is derived from a positive commandment (lav haba mik'lal aseh), and is therefore not punishable by lashes. Therefore, one who sacrifices an animal before the proper time does not receive lashes, as explained in the chapter Oso v'es b'no:4 "Omit [from the list of prohibitions punishable by lashes] m'chusar zman which Scripture expresses as a positive commandment."

The details of this mitzvah are explained in Sifra5 and in the end of tractate Zevachim.6