That's the conclusion of a new report by The Atlas Institute, a research unit of online ad technology firm Avenue A. The Seattle-based group took a look at the top 24 e-commerce stores during last year's holiday season (Nov. 25 through Dec. 24) and found that -- not surprisingly -- online shoppers work radically different from their offline counterparts. According to the study's authors, savvy e-commerce marketers can use those differences to boost their market share.

For one thing, Web shoppers are most active during the weekdays, while offline shoppers do most of their buying on Saturdays. While the offline retail world typically sees its biggest shopping day fall on so-called "Black Friday," the day after Thanksgiving, the Web's largest single shopping day was December 7, which fell on a Thursday.

The study also found that online shopping activity peaked during working hours, at around 1:00 p.m. EST.

Meanwhile, online shopping tapered off about December 15, according to the study -- perhaps indicating that shoppers doubt that items will have enough time to be shipped and received by Christmas. (Offline shopping, on the other hand, continues to increase until just before Christmas Day.)

Perhaps the most astonishing fact gleaned from the study is that online shopping from December 26 to January 2 actually exceeds the overall per-week average leading up to Christmas, suggesting there's a sizable demand for gifts that shoppers didn't receive during the holidays.

As a result of the findings, the study's authors recommend that online advertising messages and media buys be tailored to reach online consumers who are at work. Additionally, and when possible, media buyers should snap up day-part placements to target online shoppers during the middle of the workday.

E-commerce marketers that offer special holiday shipping arrangements should emphasize in their ads online ads that shoppers still have time beyond the middle of December to order gifts and have them arrive before Christmas.

Additionally, Atlas researchers said that campaigns ought to be expanded to run beyond Christmas -- to take advantage of the explosion in e-commerce during the final week of the year.

"There are a number of ways that online advertisers can take advantage of the findings in this study," said Young-Bean Song, director of the Atlas Institute. "Many retailers derive up to 50 percent of their annual revenue during the critical Q4 timeframe. Therefore, it is imperative that advertisers leverage the right tools and technologies to ensure they are most effectively reaching their customers online."