Calendar days shall be used in all computations of time made under this article 10. In computing time for any act to be done before any municipal election, the first day shall be included, and the last, or election, day shall be excluded. Saturdays, Sundays, and legal holidays shall be included, but, if the time for any act to be done or the last day of any period is a Saturday, Sunday, or a legal holiday, the period is extended to include the next day which is not a Saturday, Sunday, or legal holiday. If the time for ending the circulation of and filing nomination petitions provided by section 31-10-302, the time for withdrawing from nomination provided by section 31-10-303 (1), or the time for filing amended or new petitions to remedy objections as provided by section 31-10-305 falls on Saturday, Sunday, or a legal holiday, such act shall be done upon the preceding day which is not a Saturday, Sunday, or legal holiday.