Thanks, brosnan6, for starting this thread. ^ I read it and called MR to find out about the challenge and they made me the same offer - asking if I'd like to be Platinum immediately. Happy day....I've got a week's stay lined up for next week! Just have to make sure I get to 18.
I wouldn't have known this before....but, I was told you have to be Gold to request a Platinum challenge. YMMV