Not enough air miles!

I've made a bit of a last minute decision to head to New York for some Christmas shopping in a few weeks. I'll be going with a friend. I'm keen to treat them to the delights of UC. Because it's travelling soon we are limited but have found flights that work for us. The only problem is I'm 17500 air miles short. That is until Monday/Tuesday when my credit card statement will come through. My concern is that by then the seats will be gone. Can I hold flights and if so how long for? I don't really want to have to buy the miles, as i know i'll earn them in a few days.
Or, should I book UC out and premium back and then upgrade on Monday. (I prefer UC out I know it's the wrong direction but the club lounge in Heathrow is a real draw for me).
Thanks in advance

Ring the FC and gets seats on hold ASAP, especially if they are on a day & time which suits you. Christmas to New York is very busy and hotels are at rocket high prices. However I love it.

Explain your prob to FC and I am sure they'll be as helpful as usual.

Seconded. Many V-Flyers have had 72-hour holds before.

FYI to the OP but my October VS AMEX miles for September (statement date today) hit my FC account today.

Thanks all, my miles did post on the Saturday too! I was still 1500 short, but i bought those, to me it was worth it. It took a few attempts but I bought the first ticket in the morning. Then there were none left. So I kept refreshing every couple of hours and luckily one popped up that afternoon! Happy days. I can't wait to surprise her!