It depends on what the secret is.
Timing and flow are important, too. If there is a lot to build off of, I’d put it in 7-9. If there’s very little to build off and it’s close to the end, I’d probably say 10-12.
It really depends. I write long, 30-40 chapter stories, so I have a timeline and plan everything out before I start writing. It’s most timing and flow, but in the end, it’s up to you.