If you are on Windows go to C:\Program Files\Ultimaker Cura \plugins\PostProcessingPlugin\scripts and drop the file there (it will replace the already existing file, i had trouble getting it to work otherwise) If you're on Mac go to Applications/Ultimaker Cura, right-click on the app and select "Show Package Contents", then go to Contents/MacOS/plugins/plugins/PostProcessingPlugin/scripts (thanks u/ARegularBear
Open Cura
Click "add script" and select "Display time and layer on LCD"
Enable the checkbox