The visa stamp that is in your passport can expire while you are in the United States. The visa stamp is used only for entry into the U.S. If you leave the U.S. and plan to return but your visa stamp has expired or you have changed your nonimmigrant status while inside the U.S., you will need to get a new visa before reentering the U.S. Please note that visa stamps can only be issued outside of the United States. For more information on U.S. visas, visit http://travel.state.gov/visa/visa_1750.html.
The State Department is now publishing on its Web site the average wait times for nonimmigrant visa interviews and for the processing of nonimmigrant visa applications. The wait times are listed by post. To access the wait-time site, go to: http://www.travel.state.gov/visa/tempvisitors_wait.php.
For tips on applying for a visa, visit NAFSA: Association of International Educators web site, "10 Points to Remember When Applying for a Nonimmigrant Visa."