Fabricate has a casting time of 10 minutes.
If I was fabricating a pile of wood, feathers and stone into a pile of arrows, is it a pile of material up until the very end of the 10 minutes when it suddenly transforms? Or would it be reasonable to assume it's a continuous process of creation that is generating items, and there would be some completed product, allowing for say an archer under siege to use arrows as they are created.
The closest I can find would be the Move Earth spell, which creates things over 10 minute increments and definitely creates them continuously. but that has a duration rather than being instantaneous.
RAW seems to make it be immediate "poof" at the end of 10 minutes, which does seem less cool than magical craftsmanship (and less related to the bit about needing proficiency to create high craftsmanship items like weapons).