Yes, that's a very different question to what the original poster asked.
The question becomes one of accounting - do we need to track ammunition use at all?

One of Gary Gygax's pet games was "Outdoor Survival" and the underlying mechanism involved tracking food and water acquisition and use. Fast forward to today's RPGs, and you still find traces of this in the ways that we track equipment inventories with rations and water skins. The question becomes whether RPG players actually enjoy tracking such things.

It turns out that we have created many mechanisms for abstracting resources so that we don't have to keep a fine accounting of materials used in our games. Spellcasters have material component pouches where we just assume that the spellcaster replenishes his supplies of bat guano, feathers and whatever other materials he needs to cast his spells. Healers have healer's tools which are a "kit of bandages, herbs, and suturing tools" that the healer is assumed to replenish over time without needing to track the expenditure of rolls of bandages and doses of various herbs.

All this represents systems of abstraction intended to reduce or eliminate the accounting load placed on players. Abstracting ammunition use is just another step in this direction. Do you require players to mark off ammunition use as they fire their bows, crossbows, slings and other weapons that use ammunition? And track their purchase or craft replacement ammunition?

My experience is that players aren't really interested in keeping track of such minutiae and it's just easier to assume that their characters replenish their supply of ammunition in the same way that spellcasters and healers assume their characters replenish their supply of spell ingredients and healing supplies. They already have more than enough inventory to track, keeping lists of stuff so that they know whether they have torches, rope, iron spikes or whatever on hand when they need it during their dungeon crawl, city adventure or wilderness trek.

I'm not a big fan of accounting. I don't have characters starve to death because they forgot to add rations to their list of equipment, and I don't like the idea of characters being unable to fire their bow because they forgot to stock up on arrows the last time they were in town. It all comes down to the level of abstraction you are willing to accept in order for your game to proceed.

So the question of how many days your character needs to spend to craft additional sets of ten arrows becomes moot if you accept an additional level of accountancy abstraction.

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