You may start and stop courses as you have time. There is no requirement to take a course all in one sitting. When you stop a course and re-launch, it will ask if you want to resume where you left off, including quizzes and exams. If you lose internet connectivity, or have another technical issue which takes you out of the course, log back in and you'll be able to start right where you left off as well.
The amount of time you spend in one sitting is not timed, but the overall course may have a Seat Time Requirement. This is typically equivalent to the Course Length displayed on the course.
For CEU customers, this information is indicated by the Seat Time progress tracker on the course Detail page. For more information, see CEU: Seat Time Requirement.
NOTE: Please check out Technical Issues and FAQ if you feel there is an issue with restarting or stopping a course.