Was the significance of exact timing in the denouement of The Lord of the Rings plot discussed somewhere? Perhaps by Tolkien himself in letters somewhere?
I'm talking about Frodo and Sam arriving at mount Doom precisely as the Host of the West engaged the army of Sauron in an unwinnable battle.
Were Frodo and Sam to arrive a day later, and Gandalf, Aragon, Éomer, Gimli, Legolas and Peregrin would all be dead. Eagles would also be either dead of dispersed, and assuming the ring still gets destroyed, Frodo and Sam would also perish.
Were Frodo and Sam to arrive a day early, there would be no climactic confrontation at the Black Gate... but assuming the ring gets destroyed, Frodo and Sam would still perish, because the Eagles are nowhere near.