You will have to be aware of the following Section of the Employment Act especially (c)
60A. Hours of work.
(1) Except as hereinafter provided, an employee shall not be required under his contract of service to work:
(a) more than five consecutive hours without a period of leisure of not less than thirty minutes duration;
(b) more than eight hours in one day;
(c ) in excess of a spread over period of ten hours in one day;
(d) more than forty-eight hours in one week:
Under (c), it simply means and period of work after 10 hours will be considered as overtime irrespective of how many hours rest hours. In your case there will be 2 hours overtime although the actual hours they work are only 8.
You better clarify this point with the Labour Department before you implement it.