From http://www.united.com/page/article/0,6722,51508,00.html

Nominated Premier status for 2007 Premier benefits, and nominated Premier Associate status for 2007 Premier Associate benefits, are valid through February 2007 if nomination occurs on or before June 30, 2006; if nomination to Premier status or Premier associate status occurs between July 1, 2006 and February 15, 2007, then the respective benefits are valid through February 2008.