Has it been reported from the Prophet (peace be upon him) or the Companions that they performed voluntary prayers on Friday from the time they entered the mosque until the خطيب ascended the minbar, given that the fifteen or ten minutes preceding the Dhuhr adhan is a time when prayer is prohibited?

Continuing the supererogatory (nafl) prayer before the Jumu'ah prayer until the Khatib (preacher) arrives is not a firmly established Sunnah (definition). However, its performance has been narrated from some Companions. Therefore, one who performs it should not be condemned, and there is no blame upon one who refrains from it. As for the prohibition of supererogatory prayer on Friday when the sun reaches its zenith (qā'im al-ẓahīrah), it is a matter of scholarly disagreement.