Thanks, Snarker, that was our conclusion, too. And we worked on each line as if it were the Rosetta Stone (the original, not the on-line language course), but could never invent a through-ilne that made any kind of sense. I may have cost my friend the part because she sang the song really, really well.
The title song in La Cage aux Folles might perhaps exemplify a 9 o'clock number. It does for the first act finale - I Am What I Am - exactly what an 11 o'clock number does for the finale ultimo: rousingly primes the audience for the tour de force to come.
Imo, I think "This Time Next Year/ The Perfect Year" from Sunset Boulevard are a good example of what you mean. They're both combined at the end of the first act, one happy, the other slightly darker.
All this mention of Millers Son makes me wonder why no one has mentioned A Weekend in the Country as a good example of a 9 O'Clock number. Unless I missed it.
Art has a double face, of expression and illusion.