Apologies if this is in the wrong place, I can't put it in the Skywards question sticky.

I have miles expiring in June 2015 and just booked a return flight MAN-HKG and wanted to use miles to upgrade on the return on 18th April.

I booked a Flex Y ticket, which cost about £70 more than a Saver, but meant I could get the upgrade for about 50k miles (rather than 68k). When I came to do the upgrade, the system tells me no upgrades are currently available (either leg), try later.

I could try every day, but is there any way to find out if upgrades will at some point be allowed, or might I have to try at the airport? It would be annoying if I paid more than necessary for my Y ticket, and couldn't get an upgrade.