I think rules 13.5 and 13.6 combined cover this situation.
Since the units entering are scheduled to enter through a particular Blocking Position to enter the J Blocking Position instead of an H Blocking Position they would first have to move to the Off Map Box for J & H then move to J the next turn.
I also believe when the unit enters J they could attack immediately.
It would be recommended that this be spelled out better in the next rules update.
Thanks for your help.