You will not be able to change the time worked on any Project. dftly Time Tracker User should always Check In at the time when you start working and Check Out once you complete the work on any Project.
You can use Multi Check In page to Submit Multiple Job entries.
Note: You will not be able to edit/change the time worked on any Project once you have submitted Check In and Check Out details.
Only the person at Salesforce will be able to edit/change the Time Tracker details.