Reference development times are usually established with sensitometric testing, not just subjective trial and error. For black-and-white film, the process is tied to film-speed standards such as ISO 6 and ISO 2240.

A film is exposed in a controlled way, then its processed negative is measured for optical density across different exposure levels. Plotting density against log exposure produces the D-log H (Hurter–Driffield) curve, showing base+fog, toe, straight-line region, and shoulder. Development time is adjusted so the processed film reaches the intended contrast/index and delivers the advertised speed under the stated conditions.

So yes, measurements of density and contrast are central. Grain and visual rendering may also be considered, but the core method is objective sensitometry.

Manufacturers such as Ilford or Kodak typically use controlled lab procedures and standardized targets/measurements. Community sources like the Massive Dev Chart are different: they often compile manufacturer data plus user-submitted results. Those user times may be based on personal testing and preferred contrast/printing or scanning workflows, so they can be less standardized and more variable.

In short: manufacturer times are generally derived from controlled sensitometric testing; community-chart times may mix official data with practical user experience.