I have a Fast Flight String, have been shooting for about 3 weeks...

I'm still adjusting the brace height???

How many shots until theses things quit stretching???

My last string kept stretching despite a zillion shots it seemed! It will settle down.

There are so many variables that it's impossible to predict without more information.

I can tell you what leads to a stable string from my experience.

Endless loop
Lots of strands
Pre-stretching
String material with Vectran content

There are gobs of variables--how the string was made, how many strands, bow weight, draw length, how many shots have been put through it, if it was pre-stretched, temperature, etc. etc. etc.

Flemish strings generally settle in more than an endless string of the same strand count/material, but properly made and pre-stretched it's minimal.  Low strand count, heavy draw weight, high temps, not pre-stretched, loose twist, etc. will settle in more.

Chad

I leave mine strung for a couple of days or so..then shoot it a bit and leave a couple of more days  

That's my experience with ff.  It seems to keep stretching, unlike 450+ and the newer types....Van