Is a long rest required between uses of Arcane Recovery?

Question

The wizard class feature Arcane Recovery can be used "once per day."

Arcane Recovery You have learned to regain some of your magical energy by studying your spellbook. Once per day when you finish a short rest, you can choose expended spell slots to recover.

This seems open to multiple interpretations to me. The most obvious is that the short rest with Arcane Recovery at the end of it can't be used until after a long rest, however, any mention of a long rest is conspicuously missing. The next most obvious interpretation is that 24 hours (or a sunrise and a sunset, makes little difference to me) must pass before using it again.

During most adventures, these two interpretations are effectively the same. This would come into play on the occasion that a long rest was interrupted or skipped, especially several days in a row.

Which interpretation is most supported by the rules or developer commentary?

Answer 1

It is unclear, however I lean towards it meaning that you can use it once between long rests.

"Once per day" occurs three times in the PHB, two of which have since been errata'd to mean you can re-use it after a long rest (and must have a long rest in order to re-use it):

Drow Magic (p. 24). Here “once per day” means you must finish a long rest to cast the spell again with the trait.

Infernal Legacy (p. 43). Here “once per day” means you must finish a long rest to cast the spell again with the trait.

This leaves Arcane Recovery as the only power in the PHB to refer to "once per day" without referring to a long rest. This may be intentional, but while "once per day" is used many times in previous editions (e.g. in D&D 3.5), there has been an effort to replace it by meaning to "once per long rest" in equivalent features. This works nicely for consistency, plus in most circumstances, it works similarly, as you can take only one long rest in a 24-hour period.

Additionally, on page 11 of the Monster Manual (under "Limited Usage"), it specifies that for monster abilities, if it says "1/day", the monster must finish a long rest to use it again.

So while this may not be the rule as written, I think it is one of those things that should have been corrected to mean "once per long rest", but hasn't (yet).

Answer 2

NOTE: Leaving this up for reference, but Jeremy Crawford has indicated they do intend to publish the change that:

Arcane Recovery—"once per day" should say you have to finish a long rest between uses.

As of the November 2018 Players Handbook errata, however, this change has not been incorporated into the rules as written.

Arcane recovery does not require a long rest between uses

Recent errata have clarified when "once a day" actually means "once between long rests" for some powers - but notably not for Arcane Recovery. These edits were not done ad hoc, but in preparation for a revised printing of the Players Handbook. The errata state "Recent printings of the book include revised text that reflects the explanations here."

As Arcane Recovery still reads "once a day," I would argue the most reasonable conclusion is that this was an intentional non-edit. (NOTE: This conclusion was wrong.) So, no long rest is required between uses of Arcane Recovery.

It would be a little strange for a (long) rest to be required to gain the benefits of a (short) rest.

"Once a day" and "between long rests" are not synonyms

In the revised Player's Handbook, powers that recharge between long rests, such as Drow Magic, no longer mention "once a day." That language has been revised to read "regain the ability when you finish a long rest." (PH, Dark Elf, p. 24). The rules for recharging these powers were really changed, not clarified. There's no justification for conflating the terms "day" and "between long rests" (although a long rest may of course last until the next day has begun).

Every 24 hours isn't it either

If we take the rules at face-value, there is also nothing in the rules that says the uses of Arcane Recovery need to be greater than or equal to 24 hours apart. A wizard might use arcane recovery on Monday evening, and then on Tuesday morning, without exceeding "once a day."

So, what exactly is "a day" then?

The only tricky part remaining is to determine when one day ends and another begins. Arcane Recovery is silent on this matter, but many magic items in the DM Guide recover charges "at dawn" (see Staff of Power, DM Guide, p. 202).

(Beyond the hint we get from the DM Guide, the term "day" is undefined in the rules. In cases where the rules do not define a term, the common dictionary definition will have to suffice.)

If the availability of Arcane Recovery resets at dawn as well, that contributes to the feel of wizards and the magic items deriving their power from the same "weave of magic" (PH p. 205).

But you might choose a different time, or have different wizards regain their power at different times. For example, midnight (a.k.a., the witching hour) might be an appropriate time.

Answer 3

From the official Player's Handbook, the Arcane Recovery feature says:

Once per day when you finish a short rest, you can choose expended spell slots to recover

So first off, only a short rest is required. As for the "once per day" part, this could mean two things depending on interpretation:

1. You can only use this ability once between 12am and 11:59pm (or equivalent, if using an alternative measure of a "day")

2. You must wait 24hours (or equivalent, if using an alternative measure of a "day") before using the ability again.

I would personality interpret this the first way, as a Day is usually used in reference to a span of time rather than a duration. Also, it says "per day", not "you must wait a day", which further implies the first option.