I buy my juice at my local B&M, though they do sell online, they mix it when you order it or right there in front of you when you walk in. In case of emergencies, I use warm/hot tap water in a coffee cup and let the bottle sit until it's room temperature again shake and vape. Ideally though, I try and buy ahead and just let it sit either on my desk or in the closet, occasionally burping (taking lid off just for a moment) then shaking.
Not all need steeping though. The green apple was straight good after I got it to mix well. The lighter creams, can confirm good right out of the gate. The cereal vapes I like and heavier cream ones just keep getting better with time.
I've gotten some juice though that taste perfumie and they've been steeping and steeping and they continue to taste perfumie. They were ones I really wanted to like too... Gummi Peach and Tiger's Blood. They've been steeping two weeks, they are smelling better, but when I drip em, perfume flavor... I'm hoping further steeping will help.
I'm with you on learning DiY though. Going to start reading up. I've seen a few recipes around here that just sounded SO good.