The number, however, is a bit misleading, but I'm not completely sure how it works. If a user is currently using Facebook on their phone, a "1m" will be displayed. This "1m" remains there, I believe, until 10 minutes after the user closes Facebook--but I'm not completely sure. This also means that, when you see someone is at "2m," that really means they were active 11 minutes ago.
What I'm not 100% sure about is...does this number update when they send a message, or simply browse their newsfeed? Has anybody here run any serious tests to determine what these numbers mean?