I have a request. Rather than calculating the break taken by each employee, why don't you consider the productive time spent at work? It might sound like the same thing; however, the impact is entirely different.
Suppose you fix 8.5 hours a day x 5 days a week = 42.5 hours a week. When you calculate the productive hours spent at work, it would be far easier to keep a time track. This way, the employees would be focused on meeting the required hours to claim a productive week. Beyond that, if they take any break or even time off, it will no longer require supervision.
Furthermore, it would be easier for the managers, as they can allocate work based on the productive hours. There are several time tracking software options that you can implement based on the operations you have in your firm.