Very nice little game. I completed all the levels, and I have some notes for you. First, the music is not looping (I think), but I don't know if it was intended. Second, it took some time to figure out controls. I didn't know I could jump with Spacebar (because I tried "W" first), and the same goes with "R" to restart the level. Maybe some control manual or tutorial level would be great. Additionally, sometimes the boxes/ball didn't go back in time, even though I shot it. And lastly, try to compress the download file into a .zip file, because not everybody has .rar (just a recommendation).
But overall interesting game and fun mechanic. Graphics were good, given the short period of time we had. Would be interesting to see a bigger game with this concept :) Well done! Rated!