A turn is technically 6 seconds. So - if you are doing it by the book, 5 turns to create a weapon is only 30 seconds. I would think of it more as phases:
1st off - prep the scenario by saying that these are specially designed forges specifically for crafting the magical weapons. As such - there are forces bound here that do not exist normally in a forge.
- heating phase
- shaping phase
- cooling phase
- binding phase (where the magic is permanently bound to the weapon)
Each phase can have it's own set of encounters or problems .. maybe not continuously, but you get the idea.
During the heating and/or forging phases:
- Fire elementals or sprites come out of the forges.
- Actual fire spouts out - and the players have to stop the building/workshop from burning.
- Sabotage or ambush: Someone wants to stop this from happening before it gets too far along.
- some creatures comes up from the ground outside the workshop. Whatever they are, they are drawn to the magic "vibrations" that are rattling through the earth.
Magical binding phase:
- Not only do the players have to defend, but that have to ensure that none of the magical components (drawn runes, placed elements, etc) are disturbed.
- Perhaps someone in the forge suddenly goes mad and runs screaming towards the center of the room. (if he hits breaks the runes, then magic is unleashed in some fashion..)
- Maybe something in the room (like the floor) suddenly becomes less "material". Someone starts sinking into the floor as things start to "shift".