Amazon.com:

"Your Gold Box offers consist of great products, sold by Amazon.com or selected merchants, paired with limited-time, extra-savings coupons. We'll give you five new Gold Box offers every day. These offers are assigned based on the stores in which you've previously shopped. [...] Each Gold Box coupon expires 60 minutes after you first view it, or by clicking the "Pass forever" button, whichever is earlier."

This, along with the new NYT time-based ads, hints of a trend to an ever-changing "act NOW" commercial web. A rather clever thing to do if not pushed too aggressively.

08/06/02 update: Amazon unwraps timed discounts.

08/28/02 update: this article mentions newspaper sites which consider changing their programming according to the time of the day. MSN France sometimes promotes their soft porn section (yes, there's soft porn on MSN France), right from the front page at night.