Rails, Ruby, how to sort an Array?

 @list.sort_by{|e| e[:time_ago]}

it defaults to ASC, however if you wanted DESC you can do:

 @list.sort_by{|e| -e[:time_ago]}

Also it seems like you are trying to build the list from @messages. You can simply do:

@list = @messages.map{|m| 
  {:id => m.id, :title => m.title, :time_ago => m.replies.first.created_at }
}