There are a lot of discussions on this, and that is because of all of the variables...which even includes the thickness of the bottle wall (and its plastics composition) when being heated.  So, I don't believe their is a single answer that covers everything.  I would not look for a single answer.
For me, I do have a set steeping routine and I do take a lot of notes on each flavor.  I don't want to buy a cheap bottle of 
juice a second time simply because I didn't right it down that I tried it and it was lousy.
I do use a crock pot with all my juice bottles in zip-lock baggies so labels don't die.  The baggies tend to float on one side so I turn them over often.  It is on low heat for about 4-5 hours.
Then, cool.  Un-cap and remove the tip and let them breathe.  About every 15 minutes I put my finger over the top and shake.  I go about 8 hours of that.  Then close them up and put them in a drawer for about 4 weeks.
I buy in "blocks".  I have the block that I am currently 
vaping.  A block that has been steeping for 2-3 weeks and then the block that I just bought and is starting to steep.
What I am 
vaping this moment, I got on May 7th.  I probably ordered a block a few days prior from 3-4 vendors.
I rate on a scale of 1-5.  At 4.0, I will recommend it as okay.  At 4.5 or higher, I will buy it again.  My average for "buying again", is just under 10%.
Good luck and I hope I helped.