It's hard to blame the wizard's player for using this (annoying) strategy, when it's the optimal strategy. If there are no consequences for delays, then taking on everything at fresh full power is optimal.
So you need to introduce consequences and trade-offs. Sometimes the players get to choose whether to delay. Sometimes they can't delay (trapped behind enemy lines, constant patrols, can't rest until you're back), sometimes they must delay (after 1-2 days, you get so exhausted you just have to rest). But in many cases the players should be asking themselves "can we go on? What if we don't?"
Since your players have "learned" that they can rest at will with no consequences, if you suddenly put them in a situation where they absolutely have to keep going on, they'll be in deep trouble. The wizard will be out of spells and they'll take a hammering. You have to re-educate them.
So it could be better to start by doing a voluntary "extra effort". Say they come to a dungeon on day one, and murder the first room and then go back to rest. Next day they come to the dungeon and it's empty. Everyone's gone, and they took the treasure with them. But there's tracks they can follow. When they do, they run into some more enemies, but these turn out to be the rear guard, the main group with the treasure is up ahead. If the group rests now, the main group will be so far ahead that the PCs won't catch up. They have a choice: press on and have another fight today, or give up on the treasure. Now, resting isn't the obvious optimal strategy anymore.
A second thing to experiment with is random encounters. Random encounters have a couple of functions:
- Create the feeling the whole world doesn't revolve around the PCs and
their current plot.
- Show off the area the PCs are in by running into some signature monsters. A rock-throwing giant in the mountains, a plant monster
that tries to drag you underwater in the swamp, the annoying monkey
people in the forest that attack you from out of the trees.
- Make it unpredictable how many encounters there will be in a day.
Now you don't actually have to make them all random, as long as they seem to be so. Put on your poker face, roll dice and go "oh-oh" at the players. Don't make the random encounters more powerful than the main story ones though. A not too hard encounter that the wizard didn't count on but he's out of his best spells because he was sooo sure there'd only be one fight that day.
I think Novak makes a good point that you should also take the wizard's preferences into account. Don't enforce 4 encounters per day because it's orthodox. Some days it'll really just be one (hard) fight. Some days it'll be a couple of easier fights. Sometimes it'll be a longer than expected series of fights, and by the end everyone is running on fumes. Sometimes the PCs have the advantage and can pick their battles. Sometimes they're under pressure and stuff is just happening to them. Sometimes it's up to them to decide whether they think they can push on for gold and glory. Sometimes they're just trying really hard to set up a hidden camp because they're in wild lands and need some rest to recover.
A thing to consider with the wizard is that although canonically part of the "fun" of playing a wizard is challenging resource management, that might not be what your player signed up for. Maybe he mostly just likes being at the height of power. So he's not playing the wizard the way he's "supposed" to in a "model" game. Don't be too harsh in telling him he's wrong though. The point of RPGs is to all have fun, not to impress the internet by how correctly you're playing.
Some more ideas about different styles of time pressure:
- It can take the monsters an hour to notice the patrol hasn't come
back. If the PCs delay, the monsters go on alert. They may bring in
reinforcements so encounters are going to be harder; they're not all
waiting in separate rooms anymore. Taking on the whole dungeon at
once can be tricky.
- As (1), but the monsters go looking for the
PCs after an hour.
- As (1), but the monsters evacuate and take
their treasure with them.
- As (1), but the monsters start the
ritual early and half the prisoners are already sacrificed by the
time they burst into the boss room.
- A really big bad thing is
slowly getting closer. It's too powerful to face even with the PCs
at full strength. Only if you find the weapon that can hurt it or
the ritual that can block it's power do you stand a chance. If you
take too long to get there, it's game over. Campaign lost. You have
a couple of slack days, but every delay has to be carefully
- A PC has a nasty disease and gets sicker every day
until a cure is found.
- Every time you destroy the ghost in the
first room, it returns 1d4 days later until you find out how to lay
it to rest forever.
- In a week, the rival adventuring group will
also get to the dungeon and you'll have to fight for it, unless of
course you're already done by then.
- The PCs need the MacGuffin to
impress the king, but another group of adventurers is elsewhere also
looking for one, and might get back sooner if the PCs take their
I think the most interesting from a time/resource management standpoint are the ones where there are legitimately too many things to do in one day, but there's time pressure so you constantly have to ask "can we do one more today?".