In my experience
12 hours schedule change caused mis-connection within the award.
In that case free of change or cancel were offered.
I changed the routing.
BTW, 9 AM to 6:45 AM change is significant if the departure airport is HND/NRT. Because many people can't arrive the airport before checkin deadline by public transportaion.
In my case, I could reach at HND only 6AM or 6:10AM by the first train, 7:10AM for NRT.
IMHO, many airport have similar situation, so you have good chance of free cancelation.