I would like to know whether *to work long hours* means to make overtime or simply to work a lot of time.
Thanks in advance.
It depends on the job or profession. Teachers, in England work long hours because they spend a lot of their own time preparing lessons and marking in addition to their teaching commitments. That doesn't count as overtime as it's all unpaid. However, if you work long hours building cars, then any hours over, say, forty in a week would be paid as overtime.