It was quite some time ago, end of Jan from memory, and they specifically said when bmi leave *A so I take that as meaning May 31st in light of recent news.

They are also very slow, so make sure you email the status match request in as early as possible, but you need to trade off getting in too early as they only give you 3 months to meet the challenge!

BTW There is no reason you can't open an UA MP account and credit there for now, they'll just use that account when you request the match. Of course miles you've earned already are unlikely to count towards the challenge.