B Clam,
I'm also an ATPL/Military QFI. If your FI rating has not got a restriction (as will be the case for a B1 or higher QFI)on night flying instruction you can teach it provided you yourself are qualified and current to fly at night. Your ATPL qualifies you so as long as you are current (SEP rating and recency) as noted above you are legal. Bit of practice first might be a good plan though! Just a thought.