Do I have to complete the entire course at one time?

No. You can log out at any point during the course and the program will remember where you stopped and next time you log in you can resume where you left off. If the course has a timer, it is because the state board requires that you spend a minimum amount of time actively engaged in each lesson. It is important that you remain actively engaged and do not leave the screen idle for more than a few minutes or you may be logged out which could affect the bookmarking.