This is a decent start for a puzzle game. I liked the core game mechanic of switching between day and night to help solve puzzles. I think it might have been better to use a single key to switch, instead of two different keys, as I regularly clicked the wrong key when trying to switch. I liked that you could move with either WASD or the arrow keys, even if you only mentioned the arrows in the tutorial.
On my first playthrough, the score had a lot of decimal places. I didn't even realize there were also number of keys listed because of score covered it up. I acknowledged picking up keys, but I thought they were simply another thing to increase score. The locked doors aren't very clear in game (I thought they were up arrows at first), which made the keys seem less important at first. When I reset my game completely, my score was a whole number, which made playing easier.
The controls felt very sensitive to movement. It was really easy to move too many spaces without meaning to, even when I was actively trying to be mindful how I pressed an arrow key. It would be nice to have an option to free movement like you have now and moving only one square per button press. I would personally prefer holding something like Shift for free movement and standard movement be square based, but I could see it working the other way as well.
I think it would be helpful if there was an undo button or some other way to deal with moving a block into a corner. With how sensitive the controls are, it was easy to accidentally move a block into a space I couldn't move it out of or use it to clear a space I didn't plan to.
The contrast between the walls and spaces was a little hard to see on the day mode. There were a couple of times I couldn't figure out why I wasn't moving forward because I didn't realize there was a wall there. The contrast was much better on night mode. It is possible the issue is my monitor settings, but having an in-game way to increase the color contrast, or using a sharper contrast in general, could be helpful for some players.
There were a couple of times when I switched from day to night and visa versa, and was on a "dodge" space without being sent to a checkpoint.
You have a cool idea here and it has potential. It just needs more work.