N.O.A.A. has forecasted warmer than normal temperatures for our region this winter so you may be fine planting it any time that the weather cooperates. It sounds like this is not a small specimen and therefore should be tough enough to withstand planting/transplanting.
Just remember to mulch it with 3-4 inches and water it deeply after planting. Our soil in TX and OK does not normally freeze so watering is required when the winters are dry. Of course, water again later but at reduced levels (such as once a week or once every two weeks) if the soil feels almost dry to a depth of 3-4".
The plants should go dormant soon and loose their leaves so they will not need much moisture. However, since our winter temperatures vary wildly and winters can be dry, going dormant here is like sleeping with someone who snores.
Do not fertilize with any type of product now. Better wait and add some manure, cottonseed meal or chemical fertilizer in May and July only. Hydrangeas are not heay feeders so a little food goes a long way.
For more information, review the information on http://www.hydrangeashydrangeas.com/planting_fert.html