The extension to the congestion charge zone is coming close and my
usual drive to work will be right through it. As I work shifts there
will be times when I will be going home or starting work just as the
zone is starting / finishing.

Is there any way of knowing exactly when the zone stops operating ? If
my watch says 1830 will I still have to pay. Is there a couple of
minutes leeway or can I synchronize my watch with TFL ?

Obviously the last thing I want is a £100 fine for leaving work a
minute early ! My workplace is just outside the zone so I can get
there but it is much quicker driving direct.