Development time is not as important as many would believe. The main concern should be consistency. The accuracy of short developing times - like 3 or 4 minutes - is much more critical that longer times - like 16 or 20 minutes. The needed accuracy is more or less proportional to the total time. If you go a bit longer, you get a bit more contrast; shorter, you get a bit less. Differences in agitation can easily give development changes equal to as much as 15 percent changes in time. Therefore it is important to develop a consistent technique and then find the development times that work well for you.