Originally Posted by
jpatokal
It's around 5.5-6 hours from NRT to HIJ by train once you factor in the transfers, which sounds pretty painful after a transpac flight. Not cheap either at ~21,000 yen one way (assuming Nozomi + N'EX).
Since it sounds as if the OP has not yet made flight reservations, there's no reason not to fly in a day early, get some sleep in Tokyo, and leave for Hiroshima first thing in the morning.