Originally Posted by
economyplusfan
I haven't been able to find the answer to the following question anywhere: When is the last possible chance to upgrade an eligible fare using miles on a *A carrier?....
Requesting a Star Alliance Upgrade Award
Requests can be made after you have purchased your ticket, but must be made at least 24 hours prior to departure to allow for the partner carrier to respond to the upgrade request
http://www.united.com/page/article/0,6722,52927,00.html 