If you work for a week your timesheet can be cancelled to let your agency know.
If you don't need to submit a timesheet for a given period, for example because you didn't work you can cancel their timesheet. This lets your agency know not to expect you to submit the timesheet.
Navigate to the timesheet you'd like to cancel. Then from the bottom of the timesheet choose Cancel. You'll be asked to enter a cancellation reason to describe why the timesheet isn't needed.
If the timesheet needs to be re-opened in the future this can be done at any time by following the Resubmitting a timesheet guide. By making changes to the timesheet it will be automatically set to open until it's submitted for review.