Chart of the day: Android vs. Apple iOS, hour by hour by Philip Elmer-DeWitt @FortuneMagazine June 12, 2013, 3:11 PM EST E-mail Tweet Facebook Google Plus Linkedin Share icons Click to enlarge. FORTUNE — Here’s a curious finding from the folks at Chitika, an online advertising agency that runs mobile ads on some 300,000 websites in the U.S. and Canada. For a report released Wednesday, the company tracked roughly 300 million ad impressions hour-by-hour during the first week of May and graphed the results according to which mobile platform the visitor was using — Google’s GOOG Android or Apple’s AAPL iOS. Among the findings: Apple’s share of the traffic was 62% and Android’s 38%, despite analyst estimates that Android devices now outnumber iOS in North America. The highest volume of Web traffic occurred at 10 p.m. ET (7 p.m. PT), suggesting that the late evening hours are the most popular browsing times for both sets of users. For iOS users, however, this peak is followed by a sharp 7-hour fall-off, suggesting that Apple users tend to go to sleep at night. The decline in Web traffic among Android users, by contrast, is much more gradual, and between the hours of 4:00 and 5:00 a.m. ET actually surpasses that of iOS users.