Vedic Astrology does not arbitarily divide the day into 24 hours. Instead the true length of the day is considered from one Sunrise to another. That is why the Sunrise and the Sunset time are very important for the purpose of Vedic Jyotish.
Casting of the Ascendant, Muhurtha, and many other calculations depend on the Sunrise and Sunset time. The Sunrise and the Sunset time is different for each city depending on its position. This tool gives you the accurate Sunrise and Sunset time for your city.