Fantastic Question btw.
1. How long on average should a juice steep?
1- 1 1/2 weeks on average
2. Does the juice need to sit with the cap off for one day?
Not necessary IMO, although some think it is.
3. Does the juice need to be in a dark place? Can it be touched or sampled regularly?
Some think that light penetration can ruin your juice, although I don't believe regular incandescent bulbs will ruin your juice. Although direct sunlight on a hot day will ruin your juice.
Yes you can sample it regularly, it should not effect the steeping process.
4. Does container shape/size affect steeping time? for instance, I have a 60ml bottle of juice, if I break it up into 12 5ml containers would it steep quicker? What if I took 10ml of juice and put it in a large shallow dish, would it steep quicker as most of the surface is exposed to air?
It's possible that having smaller amounts of juice in a bigger bottle may make it steep quicker.
Not quite sure on this question.
5. does oxygen affect steeping time, or resulting flavor?
Not quite sure
6. What types of flavors need to steep longer?
Tobacco flavors, IMO this is a personal opinion question.
7. do PG/VG ratios and Nic mg effect steeping time?
It's possible the higher the VG the longer the steeping due to it being so thick.
8. What affect do temperatures have on steeping?
Well really hot temperatures can and will ruin your juice. When steeping keep it room temperature.
9. If I am mixing 2 steeped flavors, do they have to steep again?
It would make sense to, so the two flavors being mixed have time to bond
10.For DIY flavors, is there a correlation between the taste of fresh mixed juice and the taste of steeped juice. for instance, when you freshly mix a juice, do you know by the taste that it will be better once it steeps? do you know by the taste that it will be a failure reguardless of steeping?
No, I have done this many times when making juice. You can make a flavor that tastes horrid, let it steep for 1-1 1/2 weeks and its delicious.
11. When making adjustments to flavors, should you steep each time? and for how long?
Yes, but steeping should not take nearly as long.
12. juice sitting still? or juice moving while steeping?
Sitting Still
13. What is your steeping technique?
I put it in a dark room "closet for example" for 1-1 1/2 weeks. then enjoy
I hope I was able to help you. A lot of hard questions you get there, all very good questions as well, they should be placed as a sticky.
However, I do believe steeping a flavor for to long will compromise the taste of your juice. I do not recommend steeping juice for long then 1-1 1/2 weeks