Hi JoAnn,
As far as the weather goes, you are between a rock and a hard place. If you have a way to cover it (i.e. a trash can that is tall enough, or something), I would plant it sooner rather than later. With the tremendous heat we get and the expectation the drought will continue, you want to give the roots as much time to establish themselves beforehand. If we get a cold spell between now and then, cover it, and it should be alright.
Also, from past experience, I would recommend removing most, if not all, of the growing mix from around the roots. Most likely your trees growing mix is lighter than your ground soil. The roots will continue to want to grow in it (path of least resistance). Also, the ground soil will wick the water out of the growing mix. Neither of which will be good when summer rolls around in March. Make sure to check for RKN before you put it into the ground.
All of the trees I bought at local nurseries (less one that hasn't fruited yet) have all been mislabeled and have all been 'Celeste'. I never set out to buy this variety, but serendipitously, it is one of the better ones I have.
Good luck,
~james