You can lock timesheets once submitted within the Time & Expense settings of Tracker. As long as hours are submitted or approved, it should be locked. If it’s a draft or rejected it will be unlocked so hours can be updated and submitted/approved when ready.
Once the candidate submits their time, it will highlight the time entered in yellow boxes (to signify it has been submitted) and the time entry boxes will be uneditable and show as grayed out:
