In principle, there is no special allowance for working on Saturdays. Exceptions are those situations in which we can speak of overtime or irregular work, whereby employees are eligible, after all, for compensation under certain conditions.
The overtime compensation is regulated in Article H-7 of the Collective Labour Agreement. The employee is entitled to this compensation if there is an assignment from the employer and "work is carried out outside the daily working hours, determined for the employee, in so far as these working hours will be exceeded as a result". In other words, it concerns extra work, not the rescheduling of working hours.
When working with specific time slots there is presumably no question of extra work. In addition, the provision for overtime compensation only applies to employees in scales 1 through 10. We speak of irregular shifts in the case of "regular or fairly regular" work commissioned by the employer at times other than Monday through Friday between 08.00 and 18.00 hours. Article H-8 describes the allowance for irregular shifts. This allowance only applies to non-teaching employees in scales 1 through 10.
If there is no question of overtime and the employee is not eligible for an irregular shift allowance, then 'time for time' applies.