Electrolysis appointments are charged by time and how long you will need to clear an area will depend on a few factors, how dense the growth is and how high the current is.
For example, the higher the current, the quicker each individual hair will die leading to quicker clearance of an area. Also an area with a very dense growth of hair may take longer to clear than an area with only light coverage, because the hairs are each treated individually.
Regardless even on a low current the hair still dies! We just leave it in the follicle a bit longer. It will still die for good!