Mich. Admin. Code R. 423.183
Rule 183. In computing any period of time prescribed or allowed by LMA, PERA, or these rules, the day of the act, event, or default after which the designated period of time begins to run is not included. The last day of the period so computed is to be included, unless it is a Saturday, Sunday, or legal holiday, in which event the period runs until the end of the next day, which is neither a Saturday, Sunday, nor legal holiday. When the period of time prescribed or allowed is less than 7 days, intermediate Saturdays, Sundays, and legal holidays shall be excluded in the computation. Whenever a party has the right or is required to do some act within a prescribed period after being served with a document or pleading by mail, 3 days shall be added to the prescribed period. However, 3 days shall not be added if any extension of time has been granted.
Mich. Admin. Code R. 423.183