Remember to treat the inside as well as the outside. The inside will absorb more, faster.
Don't worry if one treatment doesn't do it.. let it dry, wear it a few times, maybe put it under the cushions on your couch a couple days, and add another coat; repeat if necessary... it WILL soften, be patient and don't overdo it ( too many applications).
Two or three treatments of Montana Pitch Blend got mine perfect.

Ok one more idea that worked for me. Take a piece of fur (beaver is on mine) and glue to the top edge. Trim it to the right circumference, and wide enough to put 3 to 4 inches inside and what ever you want to show outside. Smather the leather side with a good glue, insert in quiver to correct depth and fold excess over the outside. This is in addition to the break-in of course. And no broadheads don't catch. Good luck

This thread reminds me .
I had the pleasure to talk with Byron Ferguson for quite awhile and he told me some stories of Howard Hill .
This one story was about a hunting group that he was staying with in a cabin .
They asked Howard how he kept his quiver quiet and he said to put a few inches of oatmeal in the bottom and that would keep the arrows from rattling .
So all the guys did just that , and while everyone was inside eating lunch , Howard was outside pouring hot water in all there quivers ....
Byron went on about what a sense of humor Howard had and how he liked to tease his friends .

Wasn't a Hill quiver but one I have was really stiff when new.
As above I would treat and then sit on it in evenings while watching Tv.
Took just a little while and now arrows stay put with it conforming perfectly to.my back.

Eric