Benjamin Vogt has a few interesting things to say about butterfly bushes....
http://deepmiddle.blogspot.com...
The main thing that most people complain about buddlea, is that they take over in an environment where it rains a lot...
If you search the variety that you bought with the term "invasive", you will see what I mean. PA is mentioned repeatedly as one of those states where it's inadvisable to grow them.
they don't grow at my house at all... too droughty... and I have root knot nematodes...
I'd be very surprised if you couldn't plant it now, if you are still determined to grow it...
Or... just do like I do with a new plant that has been in a greenhouse, and isn't hardened off to the climate... pot it and leave it outside, bring it indoors when frost is predicted... I have lost those hot house plants to late frost... even though they were supposed to be hardy!