What is genlock idle time ?

Hello everyone,
I am wondering what is the meaning of idle time, in the genlock part of the timed monitor plugin ?
And how does it relate to the stat of stat unit for example ?

When looking at my idle time, it seems that unreal is ok, but when looking at stat unit the game time is equal to the frame time, so if I understand well unreal canno’t keep up with the rythm.
Could someone explain me the difference ?

Best,
Alexandre