This week I did initial styling on a Yew. I created some pencil sized deadwood and then wired it to give it the movement I wanted. My question is, How long will the wire need to be on the deadwood before it hardens and can be removed? It seems to be stiffening up quite a bit in only a few days. 

Not too sure, but I would leave it for at least 6 months, it is not going to bite in so no problem there! Someone else might have other suggestions.

Thank you for the reply. My concern is that typically I would treat the deadwood shortly after creating it, within a couple weeks, to protect it.
Is it ok to leave the Yew deadwood untreated for a longer period?
Also, is there a risk of the wire leaving a stain on the wood?

you can leave the Jinn for months before treating it, no I doubt the wire will stain it, and it would be easy to correct that if it did.

Wiring works by bending the branch to a new shape and letting new wood form on the outside of the branch. If the branch  is dead no new wood will form and the dead branch won't change shape.

I think bending dead wood is like what carpenters do when bending wood. Just use hot steam and pressure.

In bonsai I prefere to bend wile the branch is alive. Works every time and the risk is lower. One can always create the Jin after the mowement is created and lignified.

Thank you everyone that replied. This was very helpful. 
Peace.

Yew is a tricky one. The wood is very resistant against reshaping (Which is one of the reasons why it is a preferred wood for bows). I think just bending the deadwood with wire therefor will not hold long-term. I find that older branches that I wire into shape need multiple seasons of growth to set in shape.

Steam bending is an option.