Steeping
eliquids is all about "diffusion" per Hoosier and Kurt--who just happen to be experts on the subject.
http://www.e-cigarette-forum.com/forum/ask-veterans/158262-steeping-explanation.html#post2594434
Other than that, unless you DYI, taste your juice when it arrives--if you like it, vape it. If you don't like it, let it sit for a while... It may get better, but it may also get much worse. Eliquid flavors change with time; I like some of my favorite juices when they are very young, others taste better--to my taste buds--after a while. We're all different. YMMV. Whatever works!
Taking the cap off has nothing to do with steeping. You leave the cap off overnight only if your eliquid has an overpowering odor--alcohol, perfume, etc. and you want to get rid of that. With any luck, those offending volatile molecules will evaporate.
Happy vaping!