The mobile rewrite period lasted about a year and a half and was painful for Facebook.

The claim is about Facebook's move from HTML5 to native mobile apps (around 2011–2013). True: reliable accounts (contemporaneous reporting, Facebook engineering posts, or histories of the company) show the rewrite or transition period lasted about 18 months (roughly 15–21 months counts) and was difficult for the company, for example through slow or poorly received apps, delayed shipping or business and stock pressure. Mostly true: it was clearly painful and lasted a year to two years, but not quite 18 months (for example 12–14 or 22–26 months). Mixed: it was painful but lasted much longer or shorter, or it lasted about that long but the evidence that it was hard is weak. Mostly false: the timeline is far off (under 9 months or over 3 years) even though there was some difficulty. False: the evidence shows no such rewrite period or no meaningful difficulty.

Set before the research began.

1. E1 Facebook's Road To 'Mobile Best': HTML5, Native Apps, And Now Home TNW (The Next Web) · 6 April 2013

   “People have said the experience using the company’s HTML5-based app with a UIWebView interface was simply terrible: long load times, notifications were intermittent, and the app even crashed quite frequently.”

2. E2 Facebook's Road To 'Mobile Best': HTML5, Native Apps, And Now Home TNW (The Next Web) · 6 April 2013

   “In August 2012, Facebook released an update to its iOS app that makes it more native to the iPhone and iPad device.”

3. E3 Facebook's Road To 'Mobile Best': HTML5, Native Apps, And Now Home TNW (The Next Web) · 6 April 2013

   “But keep in mind that a month prior to Facebook’s CEO making that statement, he appeared on TechCrunch Disrupt in San Francisco in his first public appearance since the company went public and admitted that it was the company’s “biggest strategic mistake” to go with HTML5 instead of a native app.”

4. E4 The Ten Year Journey of Facebook's App for iOS InfoQ · 8 February 2023

   “Facebook rewrote its iOS app in 2012 to take advantage of native performance and improve reliability and usability over its previous HTML5-based cross-platform implementation.”

5. E5 The evolution of Facebook’s iOS app architecture Engineering at Meta (engineering.fb.com) · 6 February 2023 Own record

   “Since the app was rewritten in 2012, it has been worked on by thousands of engineers and shipped to billions of users”

6. E6 The evolution of Facebook’s iOS app architecture Engineering at Meta (engineering.fb.com) · 6 February 2023 Own record

   “Two years after Meta launched the native rewrite of the Facebook app, News Feed’s codebase began to have reliability issues.”

7. E7 Wah Blow, Pokes and an IPO: A look back at Facebook in 2012 - The Next Web The Next Web · 28 December 2012

   “Over the course of 2012, Facebook continued to iterate its mobile apps, but for a long time continued to push HTML5-enabled apps that allowed the company to sidestep many of Apple’s in-app restrictions but ended up in a terrible experience for the user.”

8. E8 Wah Blow, Pokes and an IPO: A look back at Facebook in 2012 - The Next Web The Next Web · 28 December 2012

   “Towards the end of August, Facebook finally took its iOS app native.”

9. E9 Facebook almost missed the mobile revolution. It can’t afford to miss the next big thing. Vox (Recode) · 29 April 2019

   “In early 2012, Zuckerberg redirected the entire company to focus on mobile.”

10. E10 Facebook almost missed the mobile revolution. It can’t afford to miss the next big thing. Vox (Recode) · 29 April 2019

    “As a result, the apps were buggy, slow, and prone to crashes.”

Independent sources clearly show that the HTML5 period was difficult. They describe the apps as slow, buggy and prone to crashing (E1, E10) and as a terrible user experience (E7), and Zuckerberg publicly called the HTML5 choice the company's "biggest strategic mistake" (E3). On timing, the evidence gives only scattered dates: the company turned its focus to mobile in early 2012 (E9) and the native iOS app shipped in late August 2012 (E2, E8). No quoted source says when the rewrite or transition began or ended, so the evidence does not settle whether it lasted about 18 months, and the duration part of the criteria cannot be resolved.