I hear you... Every time I buy a nursery tree that is in horrible soil I'm pondering the question as to whether the damage of repotting at a not-so-optimal time is going to be lesser than the damage done by leaving it in its terrible soil... I guess the rule of thumb is something along the lines of; "If the tree is not literally dying, it might be better to wait and repot at a better time"?
I often buy stuff just to find out. However, this is still prime time for the garden center nurseries near me - I don't find stuff like this for cheap this time of year (maybe I'm not looking hard enough), so I don't know. I suspect actively extending growth = not a good time. I'm not confident about the converse.
I'm only sure that early spring 'as buds swell' and between the summer solstice and fall equinox are okay. @jkl used to say he figured any tree could be repotted most any time IF you know what you are doing.
It's just a question of which most interests you: keeping this specific plant or finding out if it can can be repotted now. Of course it could croak delaying. I assume that it looks healthy now or you wouldn't have bought it, so I don't think it is going to croak in the next 6 weeks or so. Playing the odds, I would wait, but this would change the instant I saw it beginning to decline.