To what extent is it lawful to receive financial rewards from additional lectures delivered by faculty members outside or inside their universities during official working hours?

The university lecturer is a private employee, and his time is owned by his employer. Therefore, it is not permissible for him to work for anyone other than his employer during working hours, except with their permission. If the university he works for permits him to deliver external lectures and receive compensation for them, then there is no blame upon him; for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions."