Where the performance or doing of any act, duty, matter, payment, or thing is ordered or directed, and the period of time or duration for the performance or doing thereof is prescribed and fixed by law, the time, except as otherwise provided in sections 645.13 and 645.14, shall be computed so as to exclude the first and include the last day of the prescribed or fixed period or duration of time. When the last day of the period falls on Saturday, Sunday, or a legal holiday, that day shall be omitted from the computation.