(for KL Siew's Use Only)
You are talking about shift workers only. Are these shift workers also working on five-day week and get two rest days per week? Anyway, it shouldn't be too difficult, just follow what the non-shift workers are getting. The only thing is that their rest days are different unlike Saturdays and Sundays. Their rest days can be any day of the week like Mondays, Tuesdays..... Sundays. If you are really confused, I suggest you pay some visits to the nearby Labour Department to seek clarifications.