This graph suggests two things about advertising effects.
First, very short exposures to advertising (even just a second) can produce significant uplifts in recall and brand choice.
Second, the longer the exposure, the bigger the effect so it is worth paying more for media that deliver longer dwell times (especially if the message you need to deliver requires more time or your goal is to build some long-lasting memories for your brand). That fact that the Brand Choice line only increases slightly for dwell times above 5" might suggest that advertisers do not generally exploit this extra time to create a truly compelling experience. As ever, it is well worth developing strong creative that is more engaging than the average ad in order to produce a high return on advertising investment.
For more details, see these papers produced by Dentsu: Unlocking The New Currency of Attention and The Attention Economy.
For a debate about the topic and methodology, see this LinkedIn thread.