Time being the texture variable is the thing that took me longest to understand, and it explains almost every disappointing result.
The classic failure is a tender steak held for six hours because it was convenient. Correct temperature, correct colour, and the texture is faintly mealy. Nothing about the doneness was wrong.
So the practical rule is to treat the long hold as a feature of tough cuts rather than a convenience for all of them. If dinner slips, chill it and reheat rather than extending the bath.