Congratulations on your first game! Here is some feedback:
- the gameplay feels very slow and gets monotonous very fast. Maybe you could speed it up a notch and try to change it up a little from time to time, for example by including temporary upgrades, special enemies, events or some other abilities, that the player can use.
- it would be nice to have some indicator, how long it will take until the weapon is reloaded.
- I think it is clear that there is a lot of room for improvement regarding the visuals. At the moment, it's hard to even make out what everything is supposed to be. For example, apart from reading the description, I would not have known that I am a time traveler. I am generally a fan of games that show, don't tell, i.e. don't need a wall of text to convey information. But for your first game (and in 3 hour game jams) this is sufficient. Also, the gradient on top of the progress bars made it hard to read the text (evolution/time remaining)
- the second level was already really hard. As nardandas already pointed out, it was really easy to miss the enemies and it would take too long to reload.
- A main menu is usually better than throwing the player into a pause screen. But I guess it works too.
- If I am not mistaken, there was no way to upgrade the weapon, so it did not really fit this jam's theme. While the theme is optional and not mandatory, your game will receive more attention during the jam if it fits the theme.
- As a general hint, although you already provided a web build: for game jams, it is really beneficial to have a web build of your game. You will lose a lot of players (and therefore ratings) already, if you have to download something first
Good luck for your second game!