Weapons are a lot more consistent with SPECIAL requirements, so here's a summary for them ( italicized are single weapons): With outfits the SPECIAL requirement is usually the highest stat an outfit offers, but for outfits with no clear highest stat it is fairly random.

This post plus some of the comments (hivemind_disruptor, limeybastard) include some in-depth analysis of how crafting time is determined, and the wiki has a bunch of exact times for weapons and outfits. Basically pile as much relevant SPECIAL into the crafting room as you can, through dwellers and outfits, and definitely throw a crafting time pet in if you have one. Especially for legendary items you can make huge improvements to crafting time by having six 10 stat dwellers in the room each with a +5 or +7 outfit, plus a crafting time pet (from weeks to hours). The crafting time you see in the slot is how long it would take with the current total relevant SPECIAL in the room plus any crafting pet.

When crafting something, the room displays the item's stat like other rooms display their stat. If you tell the room to craft that item, that is the stat you then want in the room. A: In the crafting GUI where you can select a recipe to craft, in each item's slot you'll see a stat.

Fallout shelter wiki legendary junk]