Full explanation here: https://www.law.cornell.edu
Post# of 82672
(1) Period Stated in Days or a Longer Unit. When the period is stated in days or a longer unit of time:
(A) exclude the day of the event that triggers the period;
( count every day, including intermediate Saturdays, Sundays, and legal holidays; and
(C) include the last day of the period, but if the last day is a Saturday, Sunday, or legal holiday, the period continues to run until the end of the next day that is not a Saturday, Sunday, or legal holiday.