In building design, using fixed sun＇s position of a given instant of time during a summer day and a winter day can only account for two critical extreme instants and thus ignores the sun＇s dynamic behavior. A dynamic concept to describe the time duration of the sun＇s position in the sky and to determine its significance, is proposed. The concept generates the total duration of the sun at any given sky element and for any desired analysis period of time (year, season, month or day). The concept is demonstrated using a discrete calculation time interval of five minutes and 5 degrees x 5 degrees sky grid for latitude 24 degrees N. The concept is expected to provide architects with a new time duration approach to design efficient solar shading devices and to estimate solar heat gain and solar illuminance in buildings.