The time within which an act under the Act shall be done shall be computed by excluding the first day and including the last, unless the last day is a Saturday, Sunday or holiday as defined or fixed in any statute now or hereafter in force in this State, and then it shall also be excluded. If the date succeeding such Saturday, Sunday or holiday is also a Saturday, Sunday or holiday, then such succeeding day shall also be excluded.
Ill. Admin. Code tit. 50, § 8100.120