How Fast Does Mirror Sync?

The Mirror Power-Up for Trello offers live sync, but what does "live" really mean?

Updates to your mirrored card will be synced live! Work more efficiently with the ability to Mirror comments, due dates, custom fields — all in real-time!

Note: The actual time it takes to apply changes once they’ve been detected depends on the volume of changes and the response time of the tool APIs (e.g. how fast Trello can apply updates).