Pretty nice loop-based sequential puzzle, overall, in the end. Having it be a dream loop is a good way to make it make sense that certain items would carry over, though it's not always clear what you'll get to keep. Like others said I found the music loop to be pretty atmospheric and fitting to this kind of framing. I agree that the time limit per loop can end up being kinda tight, though (and "you can't come back until the loop is over" could be read as kind of a lie, given you can pause and end a loop at any time...).
I did have to wrack my brain to figure out how to get to the ladder with free inventory space -- it makes sense, knowing the intended solution, that the pool water would make the water cup undrinkable and it might just get discarded, but i arrived at an alternate solution: fill my inventory up with books so the guy just gives me the card and then go hand the books off to the librarian to get the space back. It's nice to have stuff like that be possible.
Also, i just straight up forgot the guy in the library was researching crystals till i happened to talk to him again, so i was stuck for a good while on what to actually do with the crystal -- something that might make it a bit easier to narrow down the space of options is giving NPCs that don't have any dialogue a more de-emphasized color, one that's closer to the background. After that, since there's no indication that the door in the main room has anything to do with crystals, i just had to take a wild guess with my remaining time in the loop, but that was one of the very last things i did so the number of loose ends was very small.
I don't wanna end on a negative so i just wanna emphasize the puzzle did get me actually invested enough in solving to take the time and complete it. I could even see myself coming back sometime later to optimize for time / how many loops it takes to complete everything.