You still have time before having to make a middle school decision, so there's really no downside to putting it off from your viewpoint (other than possibly having to pay to cancel?, and waiting for another appointment).
OTOH, if you want to go ahead and do the testing now, I can tell you that my ds has been tested by school without my knowledge of date/time, the day after he'd had a concussion and pulled from a class that he'd been looking forward to for months. In spite of a major headache and major annoyance, he still scored almost exactly what he'd scored on his previous IQ test.
Best wishes,
polarbear
