I wonder what the main differences are between each other and if it's just the loads how long does it cost?

The main difference that we know of between the Japanese and American Version is there are a few difference in buttons used for things. and the Lv. 1 Skeletons give 1 EXP on the JP version instead of 0 on the NA version. In any% this might save 1 second by running on the JP version.