It should be clear that a Muslim should not miss a Jumu`ah Prayer. Jumu`ah should be performed at the time of Zuhr. In exceptional circumstances, Jumu`ah may be performed before `Asr time.
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: According to the vast majority of jurists—including the scholars of the four schools of jurisprudence—the proper time for salatul Jumu`ah (Friday Prayer) is the same time of Zuhr (noon Prayer). It is, however, considered preferable not to delay it unnecessarily as the Prophet (peace and blessings be upon him) had never delayed Jumu`ah. However, since the time of Zuhr extends until the time of `Asr begins, if because of circumstances you could not perform it at the preferred time, you could still perform Jumu`ah any time before the arrival of `Asr.
According to Imam Ahmad, you can pray Jumu`ah before Zawal (the time of the sun’s zenith). If you have no choice, then you are free to follow this option. Although this view is that of the minority, it is still better than missing Jumu`ah. We must know that the Islamic Shari`ah takes into account people’s genuine hardships and circumstances, and so in face of every hardship, there is some kind of latitude and flexibility allowed in Shari`ah. So we are only making the laws of Allah hard upon us by failing to recognize the inner flexibility in the laws of Allah.