Amidst the Torah’s discussion in Parashat Tzav of the shelamim sacrifice – a sacrifice whose meat is shared by the kohanim and the person who brings the offering – it instructs that its meat may be eaten through the end of the day after the sacrifice is offered (7:16). For example, if an individual brings a shelamim to the Beit Ha-mikdash on Sunday, and it is slaughtered then, the meat may be eaten until sundown on Monday. This is in contrast to sacrifices eaten only by kohanim, whose meat may be eaten only through the night following the sacrifice’s offering. (The exception to this rule is the toda, which generally has the properties of a shelamim but may be eaten only through the following night.)
The Ramban, commenting on this law, posits that in truth, even the meat of a shelamim should preferably be consumed on the day it is offered and the following night. Although the Torah allows eating the meat of the shelamim even the next day, the primary mitzva is to eat the meat on the first day. It is only if one failed to fulfill the mitzva on its optimum standard, on the first day, that the Torah allows partaking of the meat the next day.
A number of writers raised the question of whether this kind of two-tiered model exists also with regard to the other category of sacrifices – those which may not be eaten past daybreak the morning after the sacrifice. According to the Ramban, is the primary obligation for the kohanim to eat these sacrifices on the day they were offered, before sundown, notwithstanding the permission granted to eat the meat through the night? Or, does Halakha draw no distinction between day and night with regard to the consumption of these sacrifices, and allows kohanim even optimally to eat the meat at night? According to this second perspective, it is only with regard to the shelamim that the Torah assigns two different time-periods – one within which the meat should preferably be eaten, and a later period during which the meat may be eaten if it was not completed when it should have been. When it comes to the other sacrifices, we might claim, the Ramban would agree that there is no difference between the day the sacrifice was offered and the following night, and the kohanim are not required to endeavor to finish eating the meat before sundown.
Among the sources cited in regard to this question is a seemingly innocuous remark by Rashi in his commentary to the opening Mishna to Masekhet Berakhot. The Mishna there establishes that when it comes to sacrifices which may be eaten until the next morning, “their mitzva is until daybreak” – meaning, the deadline for eating the meat is the moment when light first appears on the eastern horizon. Rashi, commenting on the word “mitzvatan” (“their mitzva”), explains, “Zeman akhilatan” – “the time when they are eaten.” It has been suggested that Rashi’s intent in this brief remark is to clarify that the word “mitzvtan” used by the Mishna should not be taken literally, as indicating that the time for the optimal fulfillment of the mitzva extends until daybreak. Rashi explained “mitzvatan” to mean “the time when there are eaten” to emphasize that the Mishna refers to the time period in which the meat may be eaten, and not when it should be eaten. As the Mishna uses the term “mitzva” in this context, Rashi feared that this might be understood to mean that even on the optimum standard, the sacrificial meat may be eaten throughout the night. He therefore clarified that the Mishna speaks of when the meat is allowed for consumption, but optimally, it should be eaten before sundown on the day the sacrifice was offered.