This question has come up before and although in the past there was some flexibility it seems that has now gone.
A SWU must be valid on the day of the flight for it to be used so in your case, no, you cannot use an expiring SWU for a March 2010 flight regardless of when it is actually pulled, even if the availability was there right now you still couldn't use it.
Occasionally you may get an AAgent willing to apply it when you waitlist, but don't be surprised if the system spots the error and pulls from the correct batch of SWU's or fails the upgrade if you have no unexpired SWU's for that date.