This is true only for a very trivial definition of "get it up". The second that Heroku starts your server all requests will be pushed over to the new dynos. For

This is true only for a very trivial definition of "get it up". The second that Heroku starts your server all requests will be pushed over to the new dynos. For a Rails app, depending on how many gems you are loading and how fast your environment can load, this might be as much as 15 seconds of request queueing.