Slots are in order of attempts. First run through took 22 minutes, played around a lot with controls and experimented with everything.
Second run was first hard attempt and running straight through (died once to boss).
Third run was deathless and I skipped all chests and upgrades (gotta go fast).
To your point on staggering, it'd be nice to know if you're about to stagger the heavy enemy, I wasn't really counting my hits and kinda mashing through (Light --> Heavy --> Slight Delay --> Repeat). I don't think it's an issue though since the attack is pretty telegraphed so I could react and dodge when I saw him raise his sword.