This was a really cool idea!
I haven't played either of the games you've listed as inspiration (though I've heard of them), but this was a fun experience and a nice twist on the theme, with using time as health and constantly dwindling resource.
I will say that I might have gotten lucky with enemy and relic spawns, but I didn't really have too much trouble with resource management - I dropped down to 1 hourglass during one of the relic defenses, but that was mostly because I was panicking a bit and used those two hourglasses when I probably could have just taken it slow and used a single instead. Then was able to just backtrack and refill.
Maybe the hourglass spawn chance or spawn locations could be reduced a bit to make things feel a little more tense, but I suppose it depends on how the team wants to flesh out the gameplay loop.
Either way I think the aesthetics, music, and SFX were all good, and the animations too, considering this being a game jam submission. All in all great work, and hoping the team can come back to at least finish out the story that's been set up!