Circadian rhythms and web analytics

Last night I fell asleep reading Chaos: Making a New Science, which I've posted about <2008/11/02/what-im-reading-chaos/">before. I woke up with that didn't-I-have-a-really-cool-dream,-oh-crap-what-was-it-about?-I'm-losing-it!-No,-I-remember! feeling. I opened up the book--I'd been reading about circadian rhythms and had had a brainstorm about applying that science to web analytics.The basics: circadian rhythms are built into plants and animals and keep us going through a 24-hour-ish period of activities (for a while, at least) even when external cues (i.e. light, temperature) are removed. Everyone has a slightly different internal clock, so if light and temperature were held steady for a long long time, we'd drift out of phase with each other. However, the cues (particularly light) sort of re-set us every day so that we're all on the same cycle. In the chaos book, they were discussing some research done with some kind of animal (it was late...I'll look it up later) where they isolated them from those regular exogenous cues, then showed flashes of light at specific points in the circadian cycle, just to see what would happen. What happened?At most points, the lights would serve to reset the circadian rhythm, sort of the way it does when we travel and have jetlag. But, at a specific point in the cycle, the animals could be thrown completely out of their circadian rhythms by these lights. They'd stay completely confused indefinitely until they were returned to the normal daytime/nighttime cycle, and then they'd get back on track.Well. This got me to thinking about how we look at website traffic. I'm pretty interested in hourly traffic (which, segmented geographically, shows some really interesting patterns...), but I'm not even going to start there. Let's think about a site where one segment of visitors returns once per week.What effect would emailing these visitors on specific days of the week have? Let's imagine that we look only at the ones who return each Wednesday. Is there a reason that they come on Wednesday? If we email them Tuesday, will they come then? If we email on Monday the next week, will they come then? Could we reset their cycle from 7 days to 6 days, meaning that we get an extra visit (extra sale?) ever 7 weeks? Or is there something about the placement of the weekend that is a more powerful cue? And, what about the ones that usually come on Fridays? Do they behave differently? Or, how about those that are in no cycle whatsoever? Is there a way we can *get* them into a cycle? Should we assume weekly, or is a 10-day cycle easier to start with? How about a 4-day cycle?