I just go by feel and that means it varies a lot. If I'm in front of the computer, my PV is used like scuba gear (hence my sigline). If I'm driving, I use it more or less steadily based on what the traffic ahead looks like or, if it's a long drive, I might feel the need to set it aside every now and then. If I'm busy, like at work or doing chores, then I go for it when I feel the need and stop after 2 to 4 minutes, when I feel I can let go for a while. I find that I can let go of it more as months from the last cig pass by when I don't have a free hand. I also find that my juice consumption is fairly steady as I smoked a lot of cigarettes in a row after work, but more steadily during weekends and do the same with vaping.
One trick I use is that I vape higher nic cigarette taste juice after meals or when I drink, else my regular low nic juice still leaves me not quite satisfied. Over time, I am also finding that a good rebuildable is perfect for all-day vape, while a Nautilus does the job for cigarette high nic juices. I can get by just fine for the occasional menthol or Tiramisu juices in a standard Aspire tank, but that does demand higher nic content than what I use in the more advanced tanks. It definitely is a matter of tinkering around in my case and I love it.
good call.