Based on what I could find on a quick search online, it looks like the final approval was not given by the Miami Gardens commissioners until mid-April 2021 (see
link). However, it also looks like the actual track layout had been finalized and published since at least January 2020 (see
link).
Even assuming UM had no indication of how the commissioners were voting until the vote took place (which, frankly, would be evidence of an even greater level of incompetence by our AD), they knew the track layout back in January 2020. A competent AD would have been in a position to start planning contingencies back then and done so. I can't fathom why the Athletic Department would need another 4 months to make this announcement.
The simplest answer may be they didn't actually need the 4 months, but were purposefully delaying the announcement to a later, more favorable time (i.e., when more tickets had been paid for, there'd be less time to do anything about it, and we'd be closer to playing games and potentially minimizing negative fan reaction). That, or it was sheer incompetence and the timing never crossed their minds because our Athletic Department is run by a bunch of unqualified suits. It's honestly a coin flip with this group.