How long is a piece of string? Simply measure the distance and divide it by about 400kts and you won't be far off. Problem is that every day, every hour, every minute is different in such a dynamic situation. Wind makes a heck of a difference and air traffic delays can pop up anywhere, any time. A flight that gets a straight-in one day might be held for 40 minutes the next..
Somebody asked what "time" is recorded for stack-leaving. It's the actual time the aircraft passes the beacon to commence approach. EATs are calculated on those times but what other agencies do with the info I do not know.