Performing one's (and sometimes not only one's) job duties in the workplace during hours not specified in the job description means overtime (overwork). Sometimes overtime is due to the high workload in the department at peak times of the year - quarter-end, holidays, etc. Sometimes the cause of overtime can be a high workload on the specialist. In either situation, the company is obligated to take into account the employee's overtime hours and pay them according to the specialist's rate, and sometimes at an increased rate if the case involves night shifts or several consecutive shifts.
The challenge for the company in the case of overtime is to be as transparent as possible in terms of hours, pay or reassignment of workload. The conditions under which an employee may overwork are negotiated in advance of hiring so that the candidate understands what the company's policy is, how often overtime occurs, and how exactly company management treats frequent overtime - whether it pays bonuses, provides extra days off, or supports mental health.