وَمِنْ شَرَائِطِهَا: الْوَقْتُ، فَتَصِحُّ فِي وَقْتِ الظُّهْرِ، وَلَا تَصِحُّ بَعْدَهُ.
Translation: Time is a condition: Jumuah is valid within Zuhr time, but not after it.
The sermon and two units of Jumuah are tied to Zuhr time. If the valid period passes, the Zuhr obligation remains instead; some other juristic traditions have different treatments of an earlier Friday start.