The issue is that the poster gets in at 5:55 and will probably have their bags before the transfer counter opens (particularly likely if their flights get in early as often happens with flights arriving early in the morning.) Last time I had checked bags on JAL, I was through customs 10 minutes after my flight arrived.

So depending, on how many bags and what time they actually get through customs, it may be quick easier to schlep the bags over to the domestic terminal. As I said, I suspect their will be a JAL agent loitering around the gate or at baggage claim that can help.