In a few groups I'm DMing, sessions last about 3h. During that time, we usually have about half the adventuring's day worth of encounters (so at level 10, about 18k XP out of the 36k XP budget). This means that the players need to keep track of HP, hit dice, spell slots etc between sessions, which has been proven to be a bit too much book-keeping (and even worse, those that do keep track of the expended resources are punished).
I don't want to just say that the adventuring day ends at the end of the session; the party will then never face situations where most of their resources have been expended.
I'm wondering if there's a way to make the adventuring day shorter, so that the XP budget becomes 50% or 75% of the regular one. I don't want to always use harder encounters: I'm already using mostly hard or even deadly ones and they also take longer that easy ones.
Is there such an official (preferable) or tested homebrew rule so that the party has fewer resources to expend and therefore have fewer encounters / lower XP budget?
Perhaps something like "get rid of hit dice healing, only allow 1 short rest per day, and get rid of 1/3rd of the spell slots".
Any proposed homebrew solutions should be supported by citing evidence or experience, per the Good Subjective, Bad Subjective guidelines.
What I'm not looking for
While relevant, this question is not about finding ways to make tracking state easier or rewarding. Even as a DM, it will make my life easier to plan each session as a day, without having to keep track how much of the budget has been expended before. Not looking for ways to speed-up combat either.