When can an artificer use the Infuse Item feature to imbue an item with an artificer infusion?

Question

While exploring Undermountain in the Waterdeep: Dungeon of the Mad Mage published adventure, the party has encountered a few monsters that are resistant to non-magical weapons. The artificer in the party wants to "infuse" the barbarian's greatsword to make them more effective at tanking. It has been about 2 hours since the party finished a long rest, and the Artificer has not used their Infuse Item feature in several days.

The somewhat ambiguous text in question from the artificer's Infuse Item feature says:

Whenever you finish a long rest, you can touch a non-magical object and imbue it with one of your artificer infusions, turning it into a magic item.

I see two ways to read this:

• Whenever means "at any time after" you finish a long rest
• Whenever means "immediately after"

Which would be the correct interpretation of RAW, and why? Assuming all other factors have been met to allow this infusion, when can an Artificer use the Infuse Item feature to imbue an item with an artificer infusion?

(The Q&A How does the artificer's Resistant Armor infusion work? goes over a bunch of information about artificers and their infusions, but does not cover the "when" answer I seek.)

Answer 1

Immediately after finishing a long rest.

This language is clarified in the Sage Advice Compendium concerning preparing spells. The Wizard's spellcasting feature says:

You can change your list of prepared spells when you finish a long rest.

The SAC goes on to clarify what this means:

Can spellcasters prepare spells not all at once, but prepare spells at various times in the day?
You prepare your list of spells only at the end of a long rest. You can’t prepare some spells at the end of the rest and then prepare more later.

So when the Artificer's infuse item feature says:

Whenever you finish a long rest

It means immediately after the long rest, in the same way that it does for preparing spells.

Answer 2

As the text says, you take those actions at the moment the long rest ends, not at some future point after the end of the long rest.

Effects that happen "when you finish a long rest" generally are either things that just automatically happen when you are rested and fresh, such as recovering spell slots, or are abstracting out specific activities that the character is taking during the down time. Keep in mind that a long rest is not all sleeping --

A long rest is a period of extended downtime, at least 8 hours long, during which a character sleeps or performs light activity... (Player's Handbook, p.186)

Within the game universe, the artificer isn't just touching objects and suddenly they're magic; instead we're abstracting away the part where he's been working on some projects in his down time, and now he's finished and the infusion is complete.

Answer 3

Immediately after a long rest

According to Merriam-Webster, the definition of "whenever" is:

at any or every time that

So when the text reads "Whenever you finish a long rest", it means "Every time that you finish a long rest". Basically, at the end of a long rest, the Artificer can infuse an item.