It is actually quite a good question in regard to developing regimens, so I hope to give a better answer, and address a little mantra of mine, in the context of thinking people need to realize that the key to success in the darkroom is being consistent enough to have verifiable cause and effect, and that that is so incredibly more important than following what some hippie from Utard advises as a time, as to be possibly one of the most under sung magic bullets yet devised.
So, the times are just my times, what I like for a particular emulsion, so they aren't meant to be holy writ, just a guide for people to start with. Also, im thinking a minute more or less in a nine minute development scheme doesn't amount to a difference most people can discerne.I probaby cooked one at nine and tried it for the other with good results and wrote it down. All of the times will in my experience yeild good usable negatives, but adjustments should be made by the individual to achieve their own version of negative nirvana. One might find 12 minutes more satisfactory, and that would be fine by me.