First arrival of new data for your empty RecyclerView.Adapter is trivial, just consume the event and you are all set. Nikola Despotoski descibes how to update the data using new handy class - DiffUtil.
Every quarter second a user spends staring at a blank screen, instead of interfacing with your app, is a quarter second more they are willing to close your app, and give their attention to something else. As such, you want to make sure that your app launches as fast as possible.