Question:

I have heard of mosques having two separate sermons in one mosque at different times. I understand the need for that with parking and overcrowding. The confusion is that the first one will be before the sun passes the zenith (before Dhuhr).

Answer:
In God’s name, to whom all praise is due…

The majority of jurists interpret a direct link between the time for the Friday sermon and prayer and the Dhuhr time, since Jumu‘ah replaces Thuhr. Many authentic hadiths indicate that the Prophet ﷺ prayed Jumu‘ah after the sun passed the zenith.

However, some scholars — including Imam al-Awzāʿī and al-Shawkānī — have held that it is permissible to perform Jumu‘ah slightly before Dhuhr time, though it is preferable to pray afterward. This opinion is supported by authentic narrations that the Prophet ﷺ occasionally prayed before the zenith due to specific circumstances.

Supporting Hadiths:

• “We used to pray Jumu‘ah with the Prophet ﷺ and then return to our homes and the walls didn’t have a shadow.” (Bukhārī 3935)

• “We used to pray Jumu‘ah with the Prophet ﷺ, then we would go home and let our camels drink and rest. Jaʿfar asked: What time was that? He replied: When the sun passed the zenith.” (Muslim 858)

• “ʿAmmar bin Yāsir led us in Jumu‘ah and there were two opinions among the congregation; some said the sun had passed the zenith and others said it hadn’t.” (Albānī, Al-Ajwiba 25)

When asked, the Permanent Committee for Fatwa in Saudi Arabia stated that the majority view is to perform Jumu‘ah after the sun passes the zenith.
Imam Ahmad and other jurists mention that performing it beforehand is valid but not preferred.

Conclusion:
Performing Jumu‘ah before Dhuhr is valid according to some opinions, but it is better and more correct to pray after the zenith.

Reference:
Assembly of Muslim Jurists of America (AMJA)
http://www.amjaonline.org/fatwa-21553/infoD