This option will only become enabled if a Client’s Profile is set to Mark Attendance Automatically. By using this option, you will be able to change the Duty From and Duty To data (i.e. the Actual Start/End Times of the Task) on the To Confirm screen. Custom Time allows you to change them to any times that you wish:
However, if you have changed the times in error, you can then select the Scheduled Time option, which resets the Duty To and Duty From data to the original Scheduled Times.