In computing any period of time prescribed or allowed by this Part, the day that the period of time begins will not be included but the last day of the period will be included unless it is a Saturday, Sunday or legal holiday, in which event the next business day will be included. Whenever a party has the right or is required to do some act within a prescribed period of time after the service of a document and the document is served by mail, three days will be added to the prescribed period of time.