Fresh post at TSA TWIC website, http://www.tsa.gov/stakeholders/transportation-worker-identification-credential-twic:
Due to the large number of transportation workers requesting extended
expiration date (EED) TWICs, TSA requests that you order an EED TWIC no
sooner than 4 months prior to your current TWIC expiration date. If
your card expires within 4 months and you would like to order an EED
TWIC, please call the TWIC Help Desk at 1-866-DHS-TWIC (1-866-347-8942).