I think you've got some excellent card game mechanics here!
In particular I really like that timeline, it's super satisfying to see what your opponent is going to do and countering them perfectly (not to mention how satisfying it is to stagger them over and over again). The horizontal positioning didn't seem as relevant in any of my games though, whenever I played as Daybreak I just ended up directly next to Cadence, and when I played as Cadence I just ended up in the corner
My thoughts for what I'd like changed kind of depend on what you want to do with this game in the future. If the goal is for this to become an in-person board game played between two actual people, then I don't have a ton of notes, but I'd definitely nerf staggering for both players.
If your goal is for this to be a singleplayer deckbuilder type game though (which I am thoroughly in favor of, this would make an excellent deckbuilder), then I definitely have some notes -- for one, I think that the opponent should always have priority. It's way more fun to respond to your opponent than to have to just guess at what's in their hand and hope that they don't just pop off out of nowhere. For another thing, I'd make it so the opponent can't stagger. Stagger is the kind of game mechanic that's really cool and fun for the person doing it, and really frustrating for the person being staggered. To make up for it, you'd have to way turn up how much damage the enemies will do, but I think it'd absolutely be worth it for gameplay. I might also simplify the enemies overall, too. When playing as Daybreak against Cadence, it's weird to see Cadence building up and managing Appeal when I don't really care about that (what does it mean for me if Cadence has 3 appeal? Sure, they might play a big card, but it isn't something like "when Cadence has 5 appeal they'll do a super powerful attack", it isn't concrete enough for me to really care)
Did also have some technical issues. All 3 of the matches I played froze at one point or another. One of them froze pretty randomly (maybe after looking in the rulebook?), one of them froze at the start of round 2 (specifically, it let me mouse over and click to play cards, at which point they'd despawn and I'd be given a new card, but none of the cards would actually resolve any effects, and there wasn't actually a Timeline in play, just a pointer), and one of them froze after I right-clicked to discard a card
I really hope I see more of this game in the future though, beyond this jam -- I'd love it if in a few years I saw a Slay the Spire-esque Tempo Battle deckbuilder (or if you'd prefer, a Tempo Battle boardgame or TCG)