Does manual time overwrite existing time records?

Yes.

You may sometimes need to edit a portion of your time. If you have forgotten to change tasks or have selected the wrong project while working, for example, for report accuracy, you may have to edit that time block within the existing time or overlapping another time entry.

Editing your existing time log will overwrite what has already been recorded in Time Doctor. Before you save, Time Doctor will send you a popup warning asking if you wish to proceed with your changes. Once you overwrite existing time in the time log, your original time is not recoverable.

NOTE: When you edit time, the entire time portion entered will be considered "edited time" and will change in color from green to yellow.

Please see this support article for more information about how to manually edit your time.