39 Miss. Code. R. 1-6-123
In computing any period of time prescribed or allowed by these rules, by order of the Commission, or by any applicable statute, the day of the act, event or default from which the designated period of time begins to run shall not be included. The last day of the period so computed shall be included, unless it is a Saturday, a Sunday or a legal holiday, as defined by statute, or any other day when the Commission's office or the Staff's office is in fact closed, whether with or without legal authority, in which event the period runs until the end of the next day which is not a Saturday, a Sunday or a legal holiday or any other day when the Commission's offices or the Staff's office is closed. When the period of time prescribed or allowed is less than seven (7) days, intermediate Saturdays, Sundays and legal holidays shall be excluded in the computation. In the event any legal holiday falls on a Sunday, the next following day shall be a legal holiday.
Whenever a party has the right or is required to do some act or take some proceedings within a prescribed period after the service of a notice, order, pleading, motion or other document upon him and the notice or document is served upon him by mail, three days shall be added to the prescribed period.
39 Miss. Code. R. 1-6-123