You're not supposed to let it sit. You're not required to do anything, besides vape it!
Never let anyone tell you that you're required to steep a juice before tasting/vaping it. If the juice is terrible fresh, it's not going to magically change into the tastiest thing ever weeks later. That's one of the biggest peeves of mine, when people tell newer people that they must not touch their juice until it sits and collects dust for any given amount of time.
I vape all of my juices fresh. Always.