Jumu`ah prayer is when the sun has passed its zenith Sahih Muslim 860 a
Arabic hadith text
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَإِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالاَ أَخْبَرَنَا وَكِيعٌ، عَنْ يَعْلَى بْنِ، الْحَارِثِ الْمُحَارِبِيِّ عَنْ إِيَاسِ بْنِ سَلَمَةَ بْنِ الأَكْوَعِ، عَنْ أَبِيهِ، قَالَكُنَّا نُجَمِّعُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم إِذَا زَالَتِ الشَّمْسُ ثُمَّ نَرْجِعُ نَتَتَبَّعُ الْفَىْءَ .
Translation
Iyas b. Salama b. al-Akwa' reported on the authority of his father
We used to observe the Friday prayer with the Messenger of Allah (ﷺ) when the sun passed the meridian. and we then returned and tried to find out afternoon shadow (of the walls for protecting themselves from the heat of the sun).