Well, the manuals usually says "minimum 40%", so if you want your engines stabilized at 40, 45, 50, 65 or whatever that's up to the flightcrew, before pressing TOGA.
"The Manuals" What Manuals?? Certainly the Boeing FCTM does not say anything about a minimum 40%. It states: "apply takeoff thrust by advancing the thrust levers to just above idle (40% N1)"
Idle thrust is about 22% N1. The wording could be better as it could be construed that 40% N1 was idle N1.