I tend to vape more mls at 18 mg than I do at 24 mg. With 18mg, I can vape all day. With 24mg, I cannot stand more than 2-3 hits in an hour's time.
There are two times that I just have to chain vape - when I'm online for an extended period of time, and when I'm driving. I have 12mg juices for those times. Two hours before bed time, I switch to my 6mg juices, so I can sleep. It's my "sleepy time" juice.