The Pause Until action pauses until criteria for conditions are met.
By default (v11.0+) Keyboard Maestro will start to conserve CPU usage of this action if it runs for a long time (after 10 seconds it will conserve a little, after 60 seconds it will conserve a lot) by only checking the condition periodically. You can turn off this feature in the action (gear) ⚙ menu.
Criteria for condition(s)
Conditions
List of Available Conditions
1. Pause Until the “Finder” app is at front, and the ⌘ key is pressed.
2. Pause Until the Mouse Is Clicked
For a discussion or other approaches, see this Forum Post.