There should be a toggle available in Projects Master where switching it ON allows Timesheet to be submitted in that Project. This will give control to the Project Manager / Admin to manage whether entry of timesheet be allowed or not in that Project. Currently, there is issue that even in "Finished" Project timesheet can be entered if the resources / categories continue to be allocated. Un-allocation of categories / resources is too much work. A simple toggle can help reduce lot of burden for users.