Paul,
The airframes themselves do not deterorate, but the other aspects of the craft do. The fuel lines go bad, the electronics, wires, electrical components, and where one metal meets another type do corrode. They would take a good rebuilding.
I am reminded of Korea where they went to the fighter aircraft <P-51s> that had been mothballed at the end of WWII, they weren't done right. And they had to be redone for the most part. The airframes were good to go, and of course the bodies, but most other systems had to be replaced.
So, the question needs to be asked,
How long to bring those aircraft online? I would say with an all out effort, with enough personel who are trained in those craft with enough parts on hand, it would take a year.
I base this on an episode of the discovery channel where they rebuild a M1, and it took them just under a year to redo and repair a battle damamged M1 tank, being that an aircraft is a bit more complex it would take a bit longer. Of course with the war footing, things could be a bit faster paced, but coupled with the volume of planes to bring online the time line stands. After all, would any nations war effort detract from the new assemblyline of current war materiel to refit old equipment. And then of course where would battle damaged equipment fit in? Would they not recover damaged vehicles to be reworked and rebuilt to be returned to the war effort?