Going to be in Tokyo in a weeks time and planning on catching the bullet train from Tokyo down to Hiroshima.

Around £129 in the green car if I book today.
Doesn't seem to let me choose a seat (not sure if it's because it's night time in Japan or what? Theres something about it cant be done before 5:30am)

Did read somewhere that sometimes getting a ticket 3 days out can be a bit cheaper? Hayatoku3?