@simrin, @anamur- I agree with @anamur. I think we should also keep in mind that a lot of these measurements are subjective. There is always an engineer that is heading a time study and he or she determines the standards of work and timing. The time study also helps a company measure the performance of employees and whether they are keeping up.
There is something called the "performance rating," for example. The engineer watches employees work, times them and comes up with the standard time that it takes for an employee to finish a job. How each employee does in comparison to that standard, is their performance rating.
So, that standard is not a random time that the company comes up with. It's still based on the employees who work there. That's why I think that a time study is a fair method to measure timing, efficiency and performance.