CODE OF CANON LAW
BOOK I. GENERAL NORMS
COMPUTATION OF TIME (Cann. 200 - 203)
Can. 200 Unless the law expressly provides otherwise, time is to be computed according to the norm of the following canons.
Can. 201 §1. Continuous time is understood as that which undergoes no interruption.
§2. Useful time is understood as that which a person has to exercise or to pursue a right, so that it does not run for a person who is unaware or unable to act.
Can. 202 §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.
Can. 203 §1. The initial day (a quo) is not computed in the total unless its beginning coincides with the beginning of the day or the law expressly provides otherwise.
§2. Unless the contrary is established, the final day (ad quem) is computed in the total which, if the time consists of one or more months or years, or one or more weeks, is reached at the end of the last day of the same number or, if a month lacks a day of the same number, at the end of the last day of the month.