Dumping Excess Altiitude

I only fly taildraggers also. When I ask ATC for instructions I can pick any airport that I want so they'll give me instructions many miles away.
The "jet-jockeys" will have a better answer.

ATC usually starts decend instructions about 100 miles out from your destination airport, +/- depending on your altitude

Orson

The "Rule of 3" usually works pretty well. To use it, you divide the number of feet you need to descend (in hundreds) by 3 to get the number of nautical miles you'll travel while doing it. Ex: FL300 takes around 100 nm, FL270 takes about 90 nm, etc. Easy math. 👍 I usually add about 10 nm to that, and start expecting ATC to begin my descent about that far from my destination. I rarely have to wait long.

Around 100 miles out is about right. But another thing is the VA i fly for requests descent at around cruise speed to save fuel. So in that case, you have to start coming down from FL360 a bit earlier and descend faster.

I usually start my descent 100-120 miles out from initial approach fix depending on my altitude. Occasionaly I go as high 39000', at that alt I start down 140 miles out 1800-2000' per min. I usually reach target alt before my IAF, you must slow down to 250kts before going below 10000', that covers some ground. You should be at target alt. before the IAF. That enables you to capture the glideslope easily.