It can take up to 90 days for USCIS to process an OPT application. The work authorization card is required to start work and to travel, so plan accordingly.
Pre-completion OPT applicants (for off-campus work before graduation) can apply no earlier than 90 days before their requested employment start date.
Graduating students can file their OPT application with USCIS no earlier than 90 days prior to the program end date and must file no later than 60 days after the program end date. Please note that if you depart from the U.S. during the 60 day period, your eligibility to apply for OPT ends upon your departure from the United States. For spring 2015 graduates the calendar below shows the application window.