Virtually all development times are empirical. The manufacturer's data in their technical data sheets are nothing more than recommendations. The basic rule is "If it works for you, it works for you!" (Courtesy of Hicks/Schultz: The B&W Handbook, which, btw, is worth reading in this context).(posted 9094 days ago)From what I understand, the designing of emulsions and of developers has something of a black magic. As a rule of thumb, one can say that strongly diluted developers act less energetic and somewhat compensating, because the active agents are quickly consumed in the dense areas of the negative and remain active in the thin (shadow) areas.
You might find some rule of extrapolation for calculating a first approximation of development times at dilutions other than the one given. However, these, too, are no more than first approximations, or parameters for a first test.