So to start, you definitely need to continue developing this, it was an amazingly fun puzzler for 48 hours.  Working through a couple of simpler levels introduction the various features and explaining them would be highly recommended.  Love these will definitely be following future development of this.

Good pacing with the increase in difficulty with each level which made it a great game to play. I wish there was a level selector in case the player gets stuck on one level like I did, but that could just be me being bad at games.

I really like this mechanic, it could definitely be made into a whole game! Since you're planning on working on it more, a few things I found frustrating were when I had to wait for a shadow to finish it's long loop to show the block I needed it to show, and when I accidentally got a block stuck on a wall/in a corner. Since you're thinking about grid movement, it might fix accidentally moving a block, but it might also be nice to have an undo, even if it was only a few per level. Also, if the cycles of the shadows stay, having some kind of fast forward might be nice so if I miss my timing I don't have to wait as long. 

Really nice, keep polishing it and I bet it'll turn out really good!

The fact that collisions are too precise, makes it hard to play sometimes and I think it'd be better to have smaller box collider, at least for movable boxes.

BTW, It's an interesting idea and it was fun to play. Well done :)

And if you had time, I'd be thankful if you play my submission <3