Two individuals do not usually take birth at the same time in exactly the same place. A mere fraction difference in time will alter the Navamsha by about 150 fractions of a degree, which would determine variations in the fulfillment of desires, relationships, spiritual enlightenment, past life, next life, the carrying forward or cancellation of past karma, the effects of past three generations of karma (loan from ancestors), the inner power and purity of soul, fame, fame of children, and so on.
In the case of twins, where the longitude and latitude are the same, the time difference in the birth of each twin will be anywhere from six to fifteen minutes, enough to significantly alter the two charts. In some cases, when two babies are connected by a skin membrane and come into the world together, the horoscope has to be made from the help of palm or thumb print, or doing a NADI reading which is available in Tamilnadu, southern India, something also known as Bhrigu Sanhita.
In the hypothetical case of two persons born at the same time a few feet from one another, the two charts for all practical purposes would appear identical. They would indicate similar psychological and physical characteristics, as well as similar life events. However, as the individuals matured, their lives would necessarily reflect different life events (dates of marriage, birth of children, occupations, deaths of parents, and so forth). These dates could be used to rectify original birth charts that would reflect true differences in birth time. Also, every horoscope always reflects the potential of the parents' stars, which would introduce differences that would distinguish the two individuals.