I was under the impression that Anki and/or Mochi already scheduled cards at resolutions finer than the day — at least by the minute. But perhaps I'm mistaken.

It does - it is easy to see when answering a new card, where the default times for the different options are <1m, <6m, <10m, 25d.

On the other hand, people do have a circadian rhythm and schedule, and learning is dependent on sleep - so it makes sense that learning plans of a given spaced repetition system do consider a day step (even if there is more resolution underlying the higher level planning).