This feature is only available in the Enterprise version of the product.
Editing time entries requires that you have the ‘Edit time entries’ permission(s) in your role
Locked time entries are ones that cannot be edited or deleted.
When a time entry is locked, its status is changed to 'Locked'. It can be checked out on the 'History' tab in Time Log.
To lock an entry you must have it marked as either billed or approved. The process is described in Billed time entries and Approved time entries, respectively.
Unlocking an entry requires making it neither billed, nor approved. It is done by editing the entry in Time Log as described here.