§1. In law, a day is understood as a period consisting of 24 continuous hours and begins at midnight unless other provision is expressly made; a week is a period of 7 days; a month is a period of 30 days, and a year is a period of 365 days unless a month and a year are said to be taken as they are in the calendar.
§2. If time is continuous, a month and a year must always be taken as they are in the calendar.
Source: Code of Canon Law (Vatican.va)