Can Sunnah prayers (Rawatib) be offered in the Mosque before the Azan is called?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. The time of the Sunnah prayers (Rawatib) starts as soon as the time of the prayer, with which they should be prayed, starts. For example, the Zuhr Sunnah can be prayed only during the fixed time of Zuhr. Now, if the person prays the Sunnah after the time of the fixed prayer starts but before the Azan is called, this is satisfactory as what important is the actual entering of the time of prayer. Allah knows best.