how is it abuse when you said
Players are to be encouraged to manage and conserve resources throughout the course of the adventuring day. It's literally the entire mechanical basis for the game. DnD after all is, mechanically speaking, a resource management game. Combat is literally HP attrition. X/ short or long rest resources.
Conserving resources during the adventuring day is different from abusing the rest mechanic and spamming Nova strikes and falling back to the 5MWD, and trying to avoid the adventuring day entirely.
Stopping the 5MWD is the DM's job in any event.
Example:
The DM sits down mid week to design an adventure for the next session or two.
Adventure synopsis: The players are [hired by a patron/ find a clue leading to/ insert hook here] stop an Evil Necromancer, who they learn has uncovered the foul Tome of Orcus, and plans to unleash a dark ritual at the ruins of the Temple of Horrors, 6 hours ride to the North.
The ritual is scheduled for midwinters eve, just 12 hours from now!
If the PCs cant stop him, all dead creatures in the surrounding 100 mile radius will arise as horrific undead, and thousands will perish.
[Now the DM draws a map and designs his encounters].
- One Very Hard 'random' encounter on the way to the ruins (with the party having enough time to Short rest after) - say the Necromancer has sent out a Demon of Orcus and undead to ambush them on the road to the temple
- [enough time to short rest, then get to and enter the dungeon]
- Dungeon entrance - Hard encounter
- Surface Room - Medium encounter
- Surface Room - Medium encounter
- PCs find stairs after that lead down to the deep Tomb under the temple, enough time to Short rest
- Tomb encounter 1 - Medium encounter
- Tomb encounter 2 - Hard encounter
- Tomb encounter 3 - Deadly encounter, BBEG
Encounters being undead, Demons, cultists and the like.
The DM can also add in a few traps or environmental challenges, maybe a few extra 'optional' encounters in a sealed off part of the Tomb (with some good loot in there as well), a social encounter or two etc.
That's how its done. Use Doom clocks enough (and be sure to spring them on the party midway through an adventure) and your players will naturally come to conserve resources and the game balances nicely.
Examples include:
- The PCs find themselves trapped in a dungeon on an island, they stopped to explore while sailing through. They need to find a way to escape before the captain of the ship leaves them for dead in 24 hours time, or they become marooned on the island.
- A mysterious tower appears in town. It the fabled tower of Zagyg, that randomly telports around the multiverse at random. Will the PCs enter and loot it before it teleports away, taking them with it?
- A BBEG plans on conduting a foul ritual. Can the PCs stop him before he completes it?
- Children have been kidnapped from the local town by monsters. The PCs lead the rescue mission. Can they save the kids, before they end up in the cooking pot, or worse?
- Bandits have been threatening the local town. PCs get word that the Bandit leader is in their camp for day. Can the PCs infiltrate the camp, and kill the leader, before he reports back to his superiors?
I could go on, but you get the idea. Frame your adventures with temporal constraints in mind (everything in the real world has temporal constraints, so to make your world come alive, so should your adventures. As an added benefit they provide win/loss conditions for the players, and drive the action and the story forwards).