At this moment it is only possible to change approved time lines by reopening them and have the resource of the time sheet make the adjustments in it. After that the time sheet needs to be resubmitted and approved. This process is a bit cumbersome.
We will develop a new feature to replace the current reopen time lines feature. It will allow authorized users to reopen approved time lines, but also edit them in bulk. This will make it a lot easier and faster to make changes to time lines.