(1) In computing any period of time prescribed or allowed by these rules or any applicable statute, the day of the act, event, or default after which the designated time period begins to run is not to be included. The last day of the period so computed is to be included, unless it is a Saturday, Sunday, or a legal holiday, in which event the period runs until the end of the next day which is not one of the aforementioned days. A half holiday is not a holiday, but is considered as a regular day.
(2) For the purpose of these rules, an item sent to the department is timely if it is either postmarked or received by the department by not later than the last day of the time period.
(3) An item which does not have a postmark is considered received as of the date it is date-stamped by the department.