Hair tends to be more likely to start in certain areas and be more tenacious in those areas, too. For instance, the first places women and men usually see facial hair (chin and upper lip) is also the toughest hair to remove permanently.
Same is true on the chest. The most common place to start seeing hairs is around the nipples and the midline (sternum). These hairs tend to be harder to get, since they appear more sensitive to the influence of androgens.
A first visit to an electrologist to remove sparse hairs on a male chest would probably take half an hour to two hours, with subsequent treatments taking much less time. Total time to completion is affected by many variables, so it’s hard to say what you might expect.