“A line manager cannot reject a submitted time-off timesheet, but needs to.”
We fixed this issue and if approver rejects the timesheet the status of timesheet turned to rejected and no more approval of the same timesheet will be seen pending at Manager.
And also we have given a feature to do unsubmit the Time offs from the Time Entry Archive earlier it was not happening.
Once you unsubmit/unapprove the Time offs from the Time Entry Archive will change the status of time offs to saved state in My Timesheet and also approved leave hours will be automatically moved to Available from Consumed.
Step 1: Submitted Leaves from My Timesheet Page.

Steps 2 :: Manager approves the Time offs and status turned to green shown in below screenshot.

Step 3::  Time off Status Page which shows Consumed (as highlighted).

Step 4:: Follow the steps shown in numerical order as shown in below screenshot to unsubmit/unapprove the Time offs from Time Entry Archive Page.

Step5: Once you do unsubmit/unapprove the Time off leave hours by updating with deselecting the checkboxes in Archive Table check with the Time off Status in My Time Off Page where you can see the consumed will be moved to Available.

Note:: If the Time off submitted/approved for week, you will be not able to unsubmit/unapprove the time offs for a particular day of selected Date in that week. Doing with Unsubmit/unapprove for one leave  from Time Entry Archive page in that week will change the status of All leaves of a week to unsubmit/unapproved.