Now that I'm doing most of my gluing during the week, I've noticed that not being systematic (or patient) can result in disaster.
Due to overwhelming praise for my deco design, I quickly started assembling another. It wasn't until I grouted the piece that I noticed a crack, right in the center of the middle piece. I figured out that this was due to my handling of the piece before it had completely dried. And then I saw a second crack, in the same spot, in the adjoining side.
Below is a rendering of what happened.
It's currently half disassembled and filthy, sitting on my work table while its fate is determined. I don't know if I should try to repair the two sides, or dunk the whole thing in hot water to release the glue so I can start from scratch.
I now have to date all of my pieces as I'm done with them to ensure that none of them are grouted sooner than two weeks.