Final decision: The **difference in local UTC times** between two synchronously aligned systems is up to a fixed offset, but the **maximum possible** such difference (in magnitude) is **8 hours**, but only if within sync window. Since 8 > 15, sync at exact opposite offsets is impossible. - Sourci

Understanding the Context

What Is Synchronous Time Alignment?

Synchronously aligned systems coordinate clocks so that they operate on a shared local UTC basis—adjusting for fixed offsets across geographic or operational locations. For example, two servers in New York and Sydney may align to a central UTC reference, applying compensating offsets to maintain consistency.

Such systems assume a fixed offset between local present time and fixed UTC time, typically ranging from −12 to +14 hours globally, depending on timezone design.

Key Insights

The 8-Hour Absolute Limit: Why Not Up to 15?

While the total time difference between any two UTC-aligned points on Earth could theoretically approach 24 hours, synchronous systems enforce strict bounds rooted in synchronization logic:

• If two systems align precisely to local UTC, the maximum measurable offset at any moment within their synchronized window cannot exceed 8 hours.
  
• Why? Because global sync protocols enforce a closed window—when two systems remain synchronized, they adjust dynamically to a common UTC offset within a bounded interval.
  
• If the offset were allowed to reach 15 hours, systems would fall outside each other’s real-time sync window, leading to desynchronization, data conflicts, or missed events.

This maximum of 8 hours is not an arbitrary constraint but a direct consequence of maintaining consistency: when all aligned systems share a common UTC offset within a fixed boundary, oscillation or drift causes sync failure beyond 8 hours of time drift.

Final Thoughts

Breaking Down the Constraint

The fixed 8-hour limit arises from:

• Clock drift management: Systems periodically correct discrepancies, stabilizing within ±8 hours.
  
• Synchronization window closure: Beyond 8 hours, time drift exceeds acceptable bounds, making mutual recognition impossible.
  
• Practical system behavior: Real-world APIs, databases, and communication protocols rely on predictable sync limits to avoid errors.

The reference to a 15-hour maximum is misleading—such a value ignores operational reality. While hypothetically possible across asynchronous or loosely aligned systems spanning hemispheres, synchronous alignment strictly caps deviation at ±8 hours.