This might seem like an obvious point - people spend more immediately after they've been paid - but it's one that I suspect is being ignored by many marketers. Time based ad serving is something that a number of companies have been experimenting with over the last few years.
The most memorable one that I've seen was for Wendy's on ESPN. From 12-2PM on Friday's, the company bought a home-page takeover and filled it with product shots of Spicy Chickens and Baconaters. Why was the perfect? Because most people who are at work at that time (at least in Canada), had a big night out and are incredibly hung over. Rationally, they want a greasy lunch to feel better. Emotionally, they want to spoil themselves for making it through another work week. Every Friday (for the 4-8 weeks the ad ran), I couldn't stop thinking about going to Wendy's. Was it because of the well-timed ads? Maybe.
But back to payday timing.
Most payrolls work on cycles. Bi-weekly or once a month. We can predict these cycles and can target based on them. A well served ad on pay day has a chance of impacting and driving sale more than one at the end of the month.
So when does your target get paid? And what will they splurge on right after the deposit goes into their account?