At least take it out of the bag! Don't know how cold it is where you are, but we have frosts, top day-time temp. 6c. I bought a couple of clematis recently & my sales guy said plant now. I think it all depends if your clematis has been raised in-doors, has it already got fresh leaves? In which case wait till the soil warms, if not you could risk it whilst it's dormant. When you plant it, make sure that you bury at least 4inches of the stem. Helps to stop clematis wilt...apparently. However, I lost two I planted last year.

Good luck!
Clang.

Thanks for the response Clang. I really appreciate it.

Pot it up in a deeper than usual pot in potting compost. If there's any topgrowth, support that with a stick for the meantime. If your weather isn't below -5 deg C, you can leave it outside, but against a sheltered wall until the weather warms up. If its colder than that, keep inside and harden off gradually over a period of days when the weather is less severe, until the weather is warmer and things are growing outside, and then plant out.

I too have bought some of these bagged clematis plants. I just opened the bag and watered them. I placed them on a flora cart under lights. I could plant them now in my zone but am waiting because of the new growth and they have not been hardened off. They have grown a lot. Good luck...