Adventuring days are no more, at least not in the 2024 Dungeon Master's Guide. The new 2024 Dungeon Master's Guide contains a streamlined guide to combat encounter planning, with a simplified set of instructions on how to build an appropriate encounter for any set of characters. The new rules are pretty basic - the DM determines an XP budget based on the difficulty level they're aiming for (with choices of low, moderate, or high, which is a change from the 2014 Dungeon Master's Guide) and the level of the characters in a party. They then spend that budget on creatures to actually craft the encounter. Missing from the 2024 encounter building is applying an encounter multiplier based on the number of creatures and the number of party members, although the book still warns that more creatures adds the potential for more complications as an encounter is playing out.
What's really interesting about the new encounter building rules in the 2024 Dungeon Master's Guide is that there's no longer any mention of the "adventuring day," nor is there any recommendation about how many encounters players should have in between long rests. The 2014 Dungeon Master's Guide contained a recommendation that players should have 6 to 8 medium or hard encounters per adventuring day. The 2024 Dungeon Master's Guide instead opts to discuss encounter pace and how to balance player desire to take frequent Short Rests with ratcheting up tension within the adventure.
The 6-8 encounters per day guideline was always controversial and at least in my experience rarely followed even in official D&D adventures. The new 2024 encounter building guidelines are not only more streamlined, but they also seem to embrace a more common sense approach to DM prep and planning.
The 2024 Dungeon Master's Guide for Dungeons & Dragons will be released on November 12th.