No FLTIME data on OSD

I set up OSD on my quad. I also included FLTIME. The value for FLTIME always stays 0.
I assume this field should give me the time since arming. All other parameters such as altitude, battery voltage, compass heading are displayed fine.
FC: Matek F405 CTR no GPS.
Is there something else that I need to activate?
I add the parameters.3 1-1-1980 01-00-00.bin.log.param (22.2 KB)