Chagigah, Chapter 1, Mishnah 6. Our Mishnah discusses the status of someone who missed the opportunity to bring his offerings on Yom Tov, and the question of how long he still has to make up what he failed to bring.
The text of the Mishnah:
"Mi shelo chag b'yom tov rishon shel chag - chogeg es kol haregel v'yom tov ha'acharon shel chag" - one who did not celebrate on the first day of the festival celebrates throughout the entire festival, including the final day of Yom Tov.
The law stated here applies to both offerings together:
The olas re'iyah (the burnt offering of appearance).
The shalmei chagigah (the festival peace offering).
If a person did not bring them on the first day of the festival - and here the reference is to the festival of Sukkos - the opportunity is not lost to him. Rather, he is given days of compensation:
All the days of the festival: he may bring the offerings on any of the seven days of Sukkos.
The final day of Yom Tov: even on Shemini Atzeres, the very last day. And although in certain respects Shemini Atzeres is considered a festival in its own right, it still serves as the make-up opportunity for the olas re'iyah and the shalmei chagigah of Sukkos.
The festival passed and he did not celebrate:
"Avar haregel v'lo chag - eino chayav b'achrayuso" - once the entire festival has passed and he has not brought his offerings, the obligation lapses and he is not required to make it up. It is indeed too late, and that is precisely how the Mishnah expresses it.
And although no further responsibility rests upon him, concerning such a person the verse in Koheles states: "Me'uvas lo yuchal liskon v'chesron lo yuchal l'himanos" - what has been made crooked can no longer be straightened, and what is lacking cannot be counted. It is too late, and there is nothing he can do about it at this point.
In summary: our Mishnah teaches that one who did not offer the olas re'iyah and the shalmei chagigah on the first day of Yom Tov may make them up on any of the days of the festival, and even on the final day of Yom Tov. But once the entire festival has passed, he no longer bears responsibility and no remedy remains for him, and of him it is said, "Me'uvas lo yuchal liskon."