Are there any statistics on time-to-rescue from when a PLB is activated to when rescuers arrive on the scene?

I realize this is _highly_ variable. But I'm curious as to whether any estimates exist: so much money is spent on the SARSAT system and SAR efforts that there must be some metrics of some kind to measure improvements/regressions over time.

(in light of the %(*&^ with the Canadian teaching ship I think some performance metrics might be of interest, and people carrying a PLB on a hiking trip in the woods need to realize that activating a PLB is not like calling 911 in a city)