Part-time personnel who are regularly employed shall be entitled to vacation leave allowances in proportion to hours worked, except that no part-time employee who does not work at least 20 hours per week and for 10 consecutive months from the beginning of employment shall be eligible for vacation allowances. Workmen on a daily wage basis, engaged or working upon detached or independent pieces of construction work, temporary in character, of the class which may be done by contractor to the lowest bidder, but which the city council has determined shall be done by day labor, shall not be entitled to the vacation allowances provided by this article. (1957 code § 1.26.010(j).)