Thank you all very much for your suggestions for far. My flight arrives NRT at 9am and departing flight to Osaka is at 6:30pm although I am trying to get onto the 4:30pm.

I guess after clearing immigration and recheck my bag onto the domestic sector (which I am assuming I can do in the morning even though the flight is not until late PM), I will probably only have 5 hours before having to head back to the airport for the 6:30pm flight.