I tried hard to get this to work too, to no avail. Apparently this feature isn't supported.
But I found a workaround in this YouTube video:
https://www.youtube.com/watch?v=BuZ8Wj3Qjdk
The workaround is to use a VLC extension called "Time v3.2". You can download it from here:
https://addons.videolan.org/p/1154032/
The extension is a zip file. When unzipped, there are two folders, "extensions" and "intf", with one file in each. Those files need to be saved in the VLC's folder. The video explains how to install the extension on Windows. I use a Mac myself, so file locations are different. On macOS, the paths where to put the extension files are:
time_intf.lua: /Applications/VLC.app/Contents/MacOS/share/lua/intf
time_ext.lua: /Applications/VLC.app/Contents/MacOS/share/lua/extensions
After copying the files to those folders, restart VLC. On macOS, open the extension from the menu VLC media player > Extensions > Time v3.2 intf.
In the dialog box that opens, enable the setting "Enable interface:" and click "SAVE!". Restart VLC.
Play some video in VLC. Reopen the extension from the menu. You can now select different meta patterns from the dropdown list, then click the ">>> USE PATTERN" button, which copies the pattern to the free-form text field. Finally, click the "START!" button, and your chosen pattern is displayed on the screen.
The string you want to enter in the field is: [T], [n], [P]%
Hope this helps anyone trying to solve this same problem.