The time for the Jumu'ah (prayer) is due when the sun declines (i.e. just after mid-day) Sahih al-Bukhari 905
Arabic hadith text
حَدَّثَنَا عَبْدَانُ، قَالَ أَخْبَرَنَا عَبْدُ اللَّهِ، قَالَ أَخْبَرَنَا حُمَيْدٌ، عَنْ أَنَسٍ، قَالَكُنَّا نُبَكِّرُ بِالْجُمُعَةِ، وَنَقِيلُ بَعْدَ الْجُمُعَةِ.
Translation
Narrated Anas bin Malik
We used to offer the Jumua prayer early and then have an afternoon nap.