@SueG3 The "+Log Time" button does not appear on the Hours tab of a project if it is marked Dead or Complete (pending those options are deactivated), and on a timesheet, the boxes are greyed out. Can you share some more details as to where these users are trying to log time?
Or are you hoping that Workfront would display the "+Log Time" button, but generate an error message saying something like "This project has been marked complete/dead, no additional hours can be logged" to make it more clear to users?