1) If you're a non-military student it's go at your own pace so there's no time limit on how long you have to complete each semester.
2) To change your username post a discussion thread in the Student Help Desk (it's located under "Support"....click on Support and then click on Student Help Desk....then click on discussions and then "actions" and then "Add new discussion") letting them know what username you want to switch to and they'll make the change for you.