It's all around coming up with ways to just tell Construct 2 to play a looping animation for a set amount of time and then do something.
You could achieve this pretty easily with timer variable of your own.
Create instance variables idleDuration and animationTimer for your sprite.
Then do events something like this:
every tick
..add dt to sprite.animationTimer
on animation 'Idle' started
.. set animationTimer to 0
animationTimer > idleDuration
.. animation 'Idle' is playing
.... do the stuff you want to do at the end of your idle animation