Oh boy, you opened Pandora´s Box againSteeping vs. not steeping is an all time classic in the vaping community I guess!
So here´s my take on it, based on my 1 year DIY experience: I did NOT have any significant change in taste through steeping (talking about several weeks), neither with my NET tobacco juices nor with my fruity juices. In the meantime I really "dirty mix" all my juices: take a 100 ml bottle, use syringes to put in the right ml amounts of the concentrates or drop in some addons like sweetener or peppermint, then pour 20 ml of base (50/50, I always keep it at room temperature) in and close and shake very well for 30 seconds. Then add base until 100 ml bottle is nearly full and shake again furiously for 1-2 minutes. Then I´m ready to go/vape.
It´s important to me that base and extracts are at room temperature to mix well, but I´ve never heated any mixture. I also shake my 100 ml "to go" bottle everytime before I refill.
Also keep in mind that vape taste is HIGHLY depending on the status of your mouth flora and mouth/nose mucosa... what you ate or drank before, if your mouth is dry ... and so on. So tasting now and compairing the taste of the same juice after 4 weeks of waiting it to steep might not be a good idea, what you´d need to do is taste both (one steeped and one freshly made batch of the EXACT same mixture) at the same time, under the same conditions.
K.
I agree that most fruit mixes don't benefit from much if any steeping. However, more complex mixes like desserts, coffees and synthetic tobaccos will change with age.