Section 20. Day, computation

A number of days specified as a period from a
  certain day within which or after or before which an act  is  authorized
  or  required  to be done means such number of calendar days exclusive of
  the calendar day from which the reckoning is made. If such period  is  a
  period  of  two  days,  Saturday,  Sunday  or  a  public holiday must be
  excluded from the reckoning if it is an intervening day between the  day
  from  which  the  reckoning  is  made and the last day of the period. In
  computing any specified period of time from a specified event,  the  day
  upon  which the event happens is deemed the day from which the reckoning
  is made. The day from which any specified period  of  time  is  reckoned
  shall be excluded in making the reckoning.