Do you mean juices you
buy, or juices you make? Most commercial juices don't require steeping unless they may be a super fresh batch, in which case you may need to wait a bit.
There is no "one" method of steeping, even in DIY, everyone has their own method. I use time, not heat, not agitation, just time and the occasional shake. I don't "air" my juices much as I use Distilled water in mine, so it may evaporate. Sometimes it's good to let them breathe, but not overmuch. Also, even in DIY you can find some stand alone flavors that are good to go, "Shake and vape" or whatever one calls them. So it's a very individual method, that new DIY folks usually need to figure out what they feel works for them best. Once you get juices in a rotation and get some backup
juice, well, I do find that just time steeping works best for me.
Unless you get very "fresh" or just mixed storebought though, there shouldn't be much need for steeping. Some custom
juice makers will make it from scratch based on what you request, and those juices often require some steep time as they are mixed to order. Hope any of this is useful.
Anna