Ash-Shu'araa • EN-AL-JALALAYN
﴿ فَجُمِعَ ٱلسَّحَرَةُ لِمِيقَٰتِ يَوْمٍۢ مَّعْلُومٍۢ ﴾
“And so the sorcerers were assembled at a set time on a certain day,”
So the sorcerers were assembled at a fixed time of a known day which was the morning of the Festival Day.