Summary:
Timecard and Timesheet are different features and they do not integrate dynamically.  That is if time is entered on the timecard it will not be updated on the timesheet and vice-versa.
 
Resolution:
There could be scenarios where you would like to update the time entered on the timecard on the timesheet for billing purpose. You will have to manually update the time entered on the timecard on the timesheet. You may then compare time entered on the timesheet and timecard by using the Compare to Timecards button on the timesheet.