During the day, I vape occasionally. I tend to use a stronger (sweeter?) flavor here, Red Bull before, now it's looking like RY4's going to replace it as my daytime vape. Every hour or two, I'll take 3-5 drags and call it good. Any more, and I find it difficult to be productive/social.
At night when I migrate to my computer/Xbox, I vape pretty solidly for several hours at a time. I usually switch to my trusty (Dekang) Vanilla, then. It's not the strongest flavor I have, but it's so damn smooth and relaxing. I've found it's a great way to wind down for the night.
I've never had any problems sleeping, by the way. I think it's a combination of my relatively low nic intake (most of my juice is 11mg) and my lighter vaping. The mellowness of the Vanilla can't be hurting, either. Dunno.