The core idea is good. There's a couple other entries that experimented with investigation as well, but I think this is an area that could use more experimentation. That said, I don't think this execution is good. You've set up a story-based setup with mechanics that encourage ignoring the story. Even if the timer isn't very strict, it still means the player have a vested interesting in skipping as much as they can. This runs completely counter to the point of investigation, which would normally be to enjoy thinking through the story. On top of that, the evidence isn't even explained to the player when they get it. I didn't finish the game, but I got 3 pieces of evidence that the items menu claimed were proof of people being related to the incident, but no indication of what the evidence actually talked about.
On a more technical side, your timer seems to go by real time passed, rather than game speed. I don't know if RMMV can support it, but such a timer is better off going by in-game time. Using the real-life time passed means that the player is punished in the case that the game lags (which was happening the entire time I had the character outside). Also, the hiding space for the brunette girl didn't make sense with the hitboxes for the other buildings.