There's no "expiration date" on a stock acquired via an ESPP creating ordinary income.
The real issue here is whether a spin-off creates another share with ESPP attributes and I've never figured out that answer, definitively. I think that's an element of Bodie7's question here.
I can't see how a pure tax free spin-off creates any obligation to recognize ordinary income if you happen to hold shares acquired via an ESPP. There's no 1099-B created in this case which is the signal that a sale has taken place.
