I figured out how to add your code to the mcu.js file, without messing up the rest of it. Now the timecode part is handled as well.
Here's the js file which should be selected as an option for the custom-module field in the Configuration Form of the O-S-C Launcher (if anyone else is interested).
mcu.js (10.4 KB)
P.S. I don't know why, but on my computer (Mojave, Cubase 10.5.20), the timecode display of mcu.json didn't work at all with the original mcu.js file.