Or HaChaim on Numbers 11:19/אור החיים על במדבר י״א:י״ט

1 לא יום אחד, "not one day, etc." We must understand the reason why the Torah describes the time the Israelites would eat meat in such detail when the gist of it could have been written in far fewer words. I believe the key to understanding this lies in our previous commentary on the second ואכלתם being a command rather than a promise. Some people can satisfy their craving for meat after having eaten meat one day, whereas others may require a far longer period on a meat diet before they have satisfied their craving. The Torah warns that even people who normally can satisfy their craving after a single day will not be allowed to do so; similarly, people who would normally require say ten days to satisfy their craving would not be allowed to do so. The respective introduction: "not one day," "not two days," etc., are to tell us that the normal manner in which these people satisfy their cravings would not apply in this instance. The limit the Torah prescribes is 30 days, at which time the meat would become repulsive. This teaches that if someone stopped eating meat before these thirty days were complete he would have violated the positive commandment of ואכלתם.