From the diamondclub.org FAQ:
Diamond Club members can continue to tier match to the Gold and Silver Executive Club tiers until 31 December 2012. After December 2012, the Executive Club will not offer any further opportunity to tier match.
If I were you I would get the match request in sharpish (provided your BA year has ticked over) and chase it up in a week or so if you haven't heard anything. Lots of these things seem to go missing and I'd hate to be unmatched at the year end.