Note that you can book a ticket for travel up to 330 days in advance, as long as you spend the miles before they expire.
It seems you're London based. My recommendation is to grab a cheap flight to the US on Norwegian. Then use the Flying Blue points to get back from the US on a Delta flight. You should be able to find availability for 25k miles (PDX-LHR is a good route) and there are no fuel surcharges if you originate in the US and fly Delta metal.