Karbala (كَرْبَلَاء, romanized: Karbalāʾ; Persian: کربلا) or Kerbala is a city in central Iraq, located about 100 km (62 mi) southwest of Baghdad, and a few dozen miles east of Lake Milh. Karbala is the capital of Karbala Governorate, and has an estimated population of 700,000 people (2015). The city, best known as the location of the Battle of Karbala in 680 CE, or the Mosques of Imam Husayn and Abbas, is considered a holy city for Shi'ite Muslims in the same way as Mecca and Medina.
Obligatory Hajj is Must on every Muslim who can perform it and no other worship can replace it. Visitation to Karbala is very great but not in stead of obligatory Hajj.
Visitation of Imam Husain (AS) in Karbala is greater in reward than recommended Hajj and Umra.
It is not allowed to break the fast before the start of the night as we read in Quran (ثم أتموا الصيام إلى الليل ) (And complete fasting till night). This is the Quranic order which can never be challenged. This is for all people who have day and night in 24 hours.
If you live in a place where there is no day and night in 24 hours, then you need to either leave the place to another place where there is day and night in every 24 hours or to follow the timings of Salah of the nearest place to you. There is question at all to follow the timings of places which very far away from your place like Makkah, Madina, Najaf, Karbala etc.