Special meetings may be called at any time, as follows:
(a) A special meeting of a three-member board of library trustees may be called by two trustees, by written notices served upon each member at least 12 hours before the time specified for the meeting.
(b) A special meeting of a five-member board of library trustees may be called by three trustees, by written notices served upon each member at least 12 hours before the time specified for the meeting.