Lack of details around ESTIMATED_WAIT_TIME metric.

Based on the available documentation, I can provide some clarity on the ESTIMATED_WAIT_TIME metric, though I acknowledge that some specific implementation details you're asking about aren't explicitly documented.

Regarding how often EWT is calculated: The Get metrics block retrieves near real-time queue metrics with a 5-10 second delay. This suggests the system is updating metrics frequently, but the exact calculation frequency or rolling window period for EWT specifically is not detailed in the available documentation.

Regarding your observation about EWT remaining static for contacts already in queue: The documentation indicates that EWT is an approximation of how long a contact will wait in queue before being connected to an agent, and metrics are only available while the contact is actively in the queue. However, the documentation does not explicitly state whether EWT is recalculated for contacts that continue waiting in queue or if it represents a point-in-time estimate that remains fixed from when the contact first enters the queue.

Your testing observation about new contacts receiving updated EWT values while existing contacts maintain their original estimate is an important implementation detail that isn't clearly addressed in the current documentation. I recommend reaching out to AWS Support directly for official clarification on these specific behavioral questions, as they would have access to the detailed implementation specifications that aren't covered in the public documentation.
Sources
Metric definitions in Amazon Connect - Amazon Connect
Flow block in Amazon Connect: Get metrics - Amazon Connect