Arkuma Slots is the casino game that takes the longest time to play; a day's worth of 10 games takes 35-40 minutes depending on fortune.
It is also the only game with no real player agency; even Rappy Slots has that little timing game after filling the rappy meter. Arkuma Slots simply gives the illusion of choice for battle games and there's never any reason not to just press A on the default target.
This makes the game a real drag to play; it is only exciting if you reach stage 21 and beyond, which over the course of a session tends to account for around 2-5 of those 35-40 minutes. The rest of the time you are mostly waiting to potentially get to the fun part.
In particular stages 1-5; I don't believe it's possible to land a battle game until stage 6, and it may even be impossible to get a no-match result in those stages, so all they are for is deciding which of the three arkuma results you get and if you hit a set bonus that early.
Getting to stage 6 presently takes about 45 seconds per game which seems trivial but per day that's 7-8 minutes and per week it's almost an hour of essentially pointless time consumption. It feels like that could be condensed.
A mechanism to make the "spinning" faster in the early game (potentially near-instant in stages 1-5) and maybe slower in the late game would mean the time requirement for Arkuma Slots overall is a bit less unfriendly, and that more of the overall playtime is spent in the interesting part.