With the native iOS app being released in 2012, the timeline would be perfect for that, yeah.
Does the mobile app take away that much usage from the web? I can see how it'll increase overall usage as people will use FB when they otherwise couldn't, but I imagine anyone who could be using it on a computer will still use the web version over a mobile app (web seems more functional, especially so with the recent Facebook/Messenger division).
A lot of workplace usage has shifted to mobile. Many workplaces will monitor all your Internet usage, and so once mobile became available, many people decided that rather than letting their employers know how much time they waste during the day, they'd use their own private Internet connection for that.
We saw a similar effect at Google with porn queries, particularly during the day. As soon as image search came to mobile Google, many porn queries moved to mobile; as of 2013 porn queries were twice as likely on mobile search as desktop.
Does the mobile app take away that much usage from the web? I can see how it'll increase overall usage as people will use FB when they otherwise couldn't, but I imagine anyone who could be using it on a computer will still use the web version over a mobile app (web seems more functional, especially so with the recent Facebook/Messenger division).