Thanks for enjoying the chaos!
I originally had it as the left mouse button, but my finger was in so much pain going to bed on Friday night after clicking thousands of times that I knew I needed to change it. I thought of making it an optional choice for the player but didn't want to inflict any pain on my players :P
The timing I knew was tricky; I was paranoid that players would be bored if shapes appeared slower. But you're probably right that I could have given them more time.