A command like that could look like this:
Begin Text Compare : [{CMDALREADYEXECUTING}] Equals '1'
Kill command, 'New Command' (by name)
End Condition - Exit when condition met
Start Indefinite Loop
Click left mouse button [duration 0.05 seconds]
Pause 1.2 seconds
End Loop
In this example I did swap the timings of the click and the pause, as you mention you want to "click the left mouse button repeatedly every 1.2 seconds".
If you instead want to hold down the left mouse button for 1.2 seconds even 50ms, you'd want to swap them back to what they are in your screenshot.