Praise be to Allah.
It is better for all Muslims to hasten to pray when they hear the adhaan, because the muezzin says, “Hayya ‘ala al-salaah (Come to prayer).” Hesitating will lead to missing the prayer.
With regard to a worker offering naafil prayers after the prayer, apart from the regular Sunnah prayers, this is not permissible, because his time belongs to someone else, according to the work contract. With regard to the regular Sunnah prayers, there is nothing wrong with him offering them, because bosses and supervisors customarily allow that.
And Allaah is the Source of strength.