Thank you for the solution. I deleted my post so you can delete yours so we don't give the answer away.
The game will probably take longer than you said because a few levels are tricky and take time and a few tries to work out.
The example in question, when you explain it, it's so obvious but I was just thinking about it differently.
That's what makes the game so much fun. It would be boring if the answer was obvious every time.