瑜伽論記 8.57

8.57

何故不言多時唯言七日等者，謂欲界中段食絕七日故，若過七日出定已其身即壞，故不得經多時。又且得爾所而方入滅定不廢多年月也，若過七日已出定其身即壞，若七日內出定其身不壞，今約不壞時為論但言七日。

Regarding why it does not speak of a longer time but only of seven days and so forth: it means that in the desire realm material food is cut off for seven days; if it exceeds seven days, upon emerging from concentration the body will perish, so it cannot last for a very long time. Furthermore, only after attaining such a state does one enter the concentration of cessation, which does not preclude many years and months; if exceeding seven days one emerges from concentration the body will perish, but if one emerges from concentration within seven days the body will not perish. Now, treating the time of non-perishing, it only speaks of seven days.