Greg Esres wrote:

I'd guess that you were OK to descend as soon as you intercepted the
inbound course,

Argh! No! The PILOT must know when he's established and within the
protected area. All you've intercepted is a navaid, not a segment of
the approach, until you've reached the start of that segment.

they intend for me to follow any altitude instructions as soon as
I'm on the course, even if I won't be inside PT limits for another 10
minutes or more.

What ATC intends is irrelevant. If they want you at the published
altitude before you reached the point where that altitude applies,
then they're got to clear you down to it, using their MVAs.

Failure to understand this concept has killed some people in the past,
including at least 1 airliner, TWA 514.

Your points are all right on. Having said that, this thread demonstrates
that, 29 years after TWA 514, both pilots and controllers do not fully
understand this stuff. The clearance for that NDB approach with "until
established" is a "setup" by ATC; albeit from lack of controller
understanding. Over the years since the TWA 514 crash the controller's
handbook has had many layers of "inner tube" patches on the area of radar
vectors to approach procedures. The only correct clearance for such a
vector to the PT area, would be for the controller to withhold approach
clearance, using MVAs, until the aircraft is within 10 miles of the PT
fix. But, this is simply not taught to controllers. The burden for this
one should be on ATC, not the pilot.