Damn, This was so much fun. I love shoot em up for these jams, especially like these, So I loved it quite a bit.
And it is really well polished, everything feels finished. Well mostly everything.
Waves I think could have more variety, more enemies, more stuff on the map, faster upgrades.
I do like the idea of every move in game costing time, that was a cool mechanic, but that does restrict the gameplay a bit, so faster upgrades could help - I think upgrades could do with a rebalancing.
Apart from that, the overall game is nice, the movement feels nice same with shooting. And the upgrades are great as well(just prefer to have them faster).
I also do love that you have a working save system, that is impressive.
Overall this was so much fun. great work!