..the passing feature keeps signal flashing for 7 seconds.
.. before the turn & they go out.
the answer is almost as confusing as the question

.. you refer to "passing" but then talk about "turning"..
imho, that is not exactly the same thing.
"Passing" is just a little lean left or right but I mostly keep going straight..
"Turning", to me, is more about going left or right from the road I'm on..
For passing or changing lanes the signal lasts about 7 seconds and then turns off..
.. that is just about right as far as I'm concerned.
.. and it seems to be true for any speed above about 24 mph.
If you are going to "turn" left or right,
and put them on while stopped,
they will stay on until just after you make the turn.
and/but ... from my experience and previous discussions:
and... on the older bikes (2001-2005), they seem to work that way at any speed.
but... on the newer bikes (2006-2010), if you put them on below about 24 mph
and are continuously de-accelerating to a full stop,
they will stay on.
But if, during that time, you decided to speed up again,
they will turn off.
2011 don't count and I don't know about the 2012's
Dennis