I use the time tracking feature which allows my staff to book weekly timesheets. However, this feature doesn't seem to lock. Is there a way to lock the time entries?

I am finding that time is being altered and then my weekly reports don't match. No matter how many times I tell staff members not to change their entries after Friday I am still finding discrepancies. What I need it to do is to lock after a certain day so that no more time can be added or changed unless it is by an admin.