The Ramadan timings for sehar and iftar varies from place to place. It is almost impossible to provide timings information about each and every place or city with accuracy. It will be good option to rely on those calendars provided by the shop owners during Ramadan as souvenir if you are living in Pakistan or to consult nearby mosque if you are living abroad to avoid any confusion regarding the timings.
However I am trying to get authentic timings of Pakistan’s major cities. Here is the Ramadan Calendar 2010-143i Hijrah showing Sehar o Iftar timings for Karachi only.