Very well understood is your concern for the practice of some employees indulging in the misuse of the concept of overtime for the sake of additional remuneration. At the same time, I am constrained to state that the sheer sense of frugality of a manager/employer should not be allowed to misinterpret the term " working hours" in respect of employees by the substitution of certain vague terms like "part of role", "wait back", "pending work" etc. Really, it can not be a matter of subjective consideration but of situational management only.
First, how would you define working hours of an employee precisely? Simply put, it is the normal hours the employee is at the disposal of the employer. Therefore, the period of time over and above the normal working hours the employee is required to be present at the work place either at the behest of the employer or because of the very nature of work assigned is over time and even the "wait back" in this regard can be over time work whether it is like an idle waiting at work place till the client dinner is over or the process of shipment is complete.
Amidst the pressure of work load, administration/management of the same is that of prioritisation only. Therefore, it is the responsibility of the manager or supervisor to prioritise the works to be attended by the subordinate employees by segregating them into urgent-ordinary, important- routine and the like so as to minimize the impact of pendency.
Fixation of realistic time-schedules and constant and effective supervision of the work of the employees is the alternative.
Personally i feel with seniority work role increases and so regardless you wait after working hours that should not be counted as OT as i have met heads of companies overseas and they have same view.
even for a growing employee not at a senior level but waits back to handle multiple roles to explore his/her caliber that should not be counted as OT although i agree HR laws may be different than my view.
I feel only when there is some urgent work that cannot wait till next day should be treated as OT.
there are 2 things when management wants employee to wait for urgent work can be OT , when emloyees want to finish their pending work which they couldnt finish in working hours should not be OT.
also if management asks employees to wait and finish back log which they should have finished in routine work hours and couldnt should not be treated as OT.
now above all is my opinion but i want to know what HR rule says.