I'm not too sure about this, but i think the employment act does have a clause which covers public holidays falling on saturdays (or rest days)
"Holidays
88. (1) Every employee shall be entitled to a paid holiday at his gross rate of pay on such of the days specified in the Schedule to the Holidays Act (Cap. 126) as fall during the time that he is employed, subject to the following:
(a) by agreement between the employer and the employee any other day or days may be substituted for any one or more of the days specified in that Schedule;
(b) if any of the days specified in that Schedule falls on a rest day, the working day next following that rest day shall be a paid holiday; and
(c) if any of the days specified in that Schedule falls on a day when the employee is not required to work under his contract of service, the employer may either pay the employee for that holiday at his gross rate of pay or give the employee a day off in substitution for that holiday. "
i only know my company practices this as a policy, and that it was a legal requirement. So if saturday happens to be a public holiday, all staff gets credited one extra day of annual leave.