First test experiment that I tried was to do a Capture Screenshot. The activation works fine and I get a cross-hair to specify what I want to capture.
Then I wanted to set things up so the captured area was sent to Graphic Converter. That worked fine. But I wanted a refinement. Graphic Converter immediately puts up a window asking if you want to retain the alpha channel with the default button Open and Retain. That is what I generally want so I set up an action for a Return Key as the next step in the Action list. That did not work as written so I put a delay (3 seconds). That worked intermittently.
Why intermittently? Because it turns out that the 3 second timer starts immediately upon launching the first action and NOT after the first action is completed. Since it takes some time just to drag out the area that you want to specify, it is easy to use up the 3 seconds before the area specification is complete.
When dragging out the area to specify for the screen capture, I have to depress the Right-Click part of the Magic Mouse. If I am depressing the Left-Click part of the Mouse, it does not work which I found peculiar because this is not the "usual" way that one specifies screen capture areas. Is this the expected behavior?
Is the delay action ( however many seconds) always timed from the very beginning of the actions rather than the completion of the proceeding action? This does not seem optimal. In the current circumstances one has to consciously complete the selection process before the timer is complete for things to work. Normally this selection process might take a variable amount of time depending, for example, on how carefully one is trying to specify the selection boundary.
BTT's screen capture capabilities are just a wrapper around Apple's screencapture command line tool.
Unfortunately I think what you encounter is the standard behavior for this and there is no way to change this.
You can run this terminal command to see the full documentation for Apple's screen capture tool: man screencapture
Keyboard Maestro offers the feature of "Pause Until Conditions are Met". Therefore, it is possible to set up the "Return Key" for "Open and Retain" to trigger only when this window appears, eliminating the need for a three-second delay. I had previously inquired about a similar function for BTT but did not pursue it since I had found a workaround for my issue at the time. Nonetheless, I believe that including such a feature would be a valuable addition to BTT's existing functionality.
This is all tickling the edges of my competence but I ran terminal with the command:
screen capture -i "somename.png" and it worked. It provides me with a cross-hair to select area on the screen. But it does not matter if I "Click and Hold" the "Left" or the "Right" part of my Magic Mouse. Both work.
But for some reason, when I activate this action with BTT then holding on the "Left" area for the "Click and Hold" it does not work. The cross-hair has appeared and I can move it but it does not sweep out an area to be captured. Holding down the "Right" area does work.
I can learn this behavior but for me it is not the expected.