14 Ill. Adm. Code 555.80
Computation of Time
Section 555
Section 555.80 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, federal or State holiday. Timeliness shall
be deemed the date of postmark or the date of hand delivery.