What do the platforms' own creator/advertiser pages say about hooks, pacing and opening seconds for vertical short video, and what do they actually show as evidence?

TikTok's advertiser best-practice page recommends a hook/body/close structure and states that 90% of ad recall impact is captured in the first six seconds, citing an internal TikTok Creative Guide (2020) without methods on the page. Curator qualifications: The figure concerns ad recall for advertisers, not retention in organic storytelling; do not generalise to narrative pacing. YouTube Shorts help pages (S12/S13) not reinspected; Get feedback criteria undefined per producer. No independent measurement; platform self-reported marketing research. Limitations: Advertiser marketing page. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.tiktok.com/business/en-US/blog/creative-best-practices-top-performing-ads",
      "note": "TikTok business blog section 4 (Hook bullet) and Sources list"
    },
    {
      "url": "https://support.google.com/youtube/answer/10059070",
      "note": "TikTok business blog section 4 (Hook bullet) and Sources list"
    },
    {
      "url": "https://support.google.com/youtube/answer/9314415",
      "note": "TikTok business blog section 4 (Hook bullet) and Sources list"
    }
  ]
}