Good evening and welcome to Just Answer,
Sorry to hear that the envelope was not delivered to Ann Arbor as expected. Many reasons why it was not delivered (thinking weather might have something to do with this). As for what to do next, check first with the USPS online site as entering in the tracking number will give you both some understanding where the envelope is right now:
Since the post office in both Jacksonville and Ann Arbor will be closed tomorrow, going into the office first thing Friday morning would be my next suggestion as speaking to the postmaster and not clerical should give you a better understanding if the envelope does not arrive on Friday the earliest.
I hope that this information was found helpful as also if you could take a second to rate my assistance so that I know my help was found useful tonight.