14 Ill. Adm. Code 515.100
Computation of Time
Section 515
Section 515.100 Computation
of Time
Computation of any period of
time prescribed by this Part shall begin with the first business day following
the day on which the act, event or development initiating that period of time
occurs, and shall run until the end of the last day or the next business day if
the last day is a Saturday, Sunday or federal or State holiday. When the
period of time is 5 days or less, Saturday, Sunday and federal or State
holidays shall be excluded in the computation of time. Timeliness shall be
determined by the date of postmark or the date of hand delivery.