Steeping tends to improve flavor, yes. I would say some juices seem to need less steeping than others, such as fruits and berries. Others will need a longer steeping time. If you post your recipes, I'm sure that some folks in the DIY forum can help you.
With that said, if in doubt (or using a complicate recipe) I'd say that steeping is a good idea. I will taste (on my tongue) mixes after about 24 hours just to make sure that nothing is going horribly wrong, but I won't vape anything for at least a week. I know that is harder with your FIRST flavor mixes, but the consensus seems to be that not waiting and steeping may lead to early disappointment, adding more flavor, then over-flavored mixes. I usually will NOT taste or modify a mix for at least a week. I just put them in my closet where it's usually dark and cool, and shake them a couple times a day.
If you do vape them, remember that they are far from "finished" and amending them at THIS point may set you up to fail later if you think you need to "add" anything because you won't really know without a steep time. If you have a berry dominant flavor and have to "try" something, I'd probably recommend that, although it too will probably change.
Best of luck. There are various methods to reduce steeping time but other than shaking, I don't tend to use them. Now that I have a steady routine for preparing as I need flavors, I find the simplest method to be time, as heat can be overdone and "dull" mixes or denature nicotine and etc.
Best of luck, I hope they turn out great
Anna