I'm guessing you're arriving at KIX at around 8:30AM and leaving NRT at around 18:00PM.

You have ample time for a bus ride to ITM to catch the midday ITM->NRT JAL flight, as well as catching the midday KIX->HND JAL flight then changing to a bus to NRT, so I guess time is not an issue (no need to rush for either). Both of these buses take roughly the same time for the transfer, however the bus from KIX to ITM is 1,700 yen, while the bus from HND to NRT is 3,000 yen so you save some yen if you do the KIX-ITM-NRT route.