"Direct when able"

When instructed to fly a heading then "Direct XYZ when able", does a
controller expect a call when you are in fact able and will be turning
on course? Usually it is a trivial turn since the heading they give is
a good guess for direct course.

I've had conflicting experience. One time after being told the above,
I responded "I'm able to go direct now" and his ackowledgement had a
"who cares? Just do it" tone to it.

Just a few days ago, I made the 8 degree turn to navigate directly to
the VORTAC, and when the shift change at approach took place, the new
controller asked what my heading was, whether I was picking up the
VORTAC, and when I told him that I was navigating direct, he seemed
surprised.

Mitchell Gossman
St. Cloud, Minnesota