While the wording says "has demonstrated the ability to instruct at night", I would hope it would be a bit more.
In my case [I did it as part of my FI course, not separately] it was
- An overview of the night rating syllabus that I would have to teach
- The board briefs for the night exercises
- The patter for the night circuits both received and returned.
The FI instructor also played ham-fisted student botching a couple of flares. No idea how long it took exactly, an hour to hour and a half sounds sensible if all goes well, with maybe 3-4 hours ground time.