Alright, cool concept you got here. You obviously didn't have time to make the monsters actually attack you, but that's fine. It's a game jam. Here are three tips that don't take much time to implement but would have improved the game a lot:
1. I play on a 4K monitor, and the text at the top left corner was tiny. On your canvas there's a component called Canvas Scaler. If you set the variable UI Scale Mode to "Scale With Screen Size" all the UI elements will scale based on the user's resolution.
2. Remember to give the player feedback to inputs. When I click to shoot or to change the time scale I need to know that my input actually got registered. All you need to do is record some simple sound effects and play them when the player presses these buttons. Here's a very useful guide to audio in Unity:
3. Add an option to close the game without having to press alt + f4. The super simple way is to add a PauseMenu object that is inactive in your canvas, and when the player presses escape this gets set to active. In the pause menu, all you need is a button to continue the game and a button to quit. Application.Quit() will close the game.Good luck next game jam! :)