I think the idea is development to completion, I read an article written by William Mortensen in which he discusses the process. In the case of very old film, unknown development times, just let the film develop to max densities, no need to worry about how long in the developer. Color film has less silver as it uses color couplers which add to the density, the long cold stand will hopely develop all the silver in the film adding density. I have experimented with the long cold stand, got some nice negatives, just not worth the trouble.