No, there is no magic number, because someone whose tires last 50k can’t rotate them the same way as someone whose tires last 80k. And they aren’t rotated once, they are rotated 3 times. That way the tires wear evenly, the uneven wear is removed and everything works, more or less.
I explain it here:
Morrillu: I would only rotate them on all-wheel-drive cars to avoid damaging the power distribution.