I recently purchased the 1947s and was also in your position.
I soaked mine in hot water for 3 hrs and from what I can remember, did not lose much indigo. I got a 32 x 32 and it shrank to 29.5 x 30, but has since stretched out to a 30 to 30.5 after wearing.
I believe the longer you soak, the more shrinkage you will get and cold soaking will supposedly lose less indigo, though my chief concern was to get maximum shrinkage.
The vinegar will help keep in the indigo so...