I want to say that it took 3-4 days for me to get the achievement. I know I went through several board setups before I finally found one that didn't fail overnight. What Fiskbit is suggesting sounds very similar to what I used, but I can't fully recall.
This reminds me, I need to get the rest of the story achievements. I have all of the gameplay related ones, but only about half of the ones for the story. A level finally frustrated me to the point that I put it on hold and later forgot about it. I was more into the Custom Games.
Steam reports 122 hours on this one, only about half of which was idling for achievements. I more than got my money's worth out of this one! I still hope that it somehow becomes a huge hit and gets the recognition it finally deserves. It's by far the best puzzle game I've ever had the great pleasure of playing.
You know what? A few rounds before bed sounds like a good idea...
OH NO! My save is gone!
Probably wouldn't hurt to start over, anyway. It's been so long, I'm sure I've forgotten the story and certain nuances of the gameplay.