Typically a cow will dry up within a couple of weeks and be totally dry by 4-6 weeks. Unless she is milking very heavy at weaning time, mastitis isn;t genrally a problem with beef cows.
That said, we keep an eye on the cows for a week or 2 post weaning to insure that the udder is decreasing and doesn;t appear hard/full or hot. Just a paranoid precaution since we've never had a cow develop a problem.
dun