The rules of issuing a US visa change constantly and depend on occurrence of War, civil unrest; security concerns, natural disasters but they are for a temporary period in a certain country. Individuals from any of the countries where there is no consular presence can avail the services from the nearest embassy. The US Department of State website periodically updates the status of visa services provided.
A visa permits arrival at a port of entry and subsequently a request can be made to the Department of Homeland Security. The Customs and Border Immigration Official decide the tenure of the stay. They can refuse entry if the stated information and facts provided for visits are incomplete or wrong. In Refusal of entry visa fee is not refunded.
US Immigration officials work with the target to complete all applications within 4 months but this is not a guarantee. There are seasonal high and low which affect the waiting time as every application has unique traits and requires different treatment and approaches. Additional administrative checks take a long time and delay the proceedings. The time allotted to live and work in USA on a temporary visa is decided on the strength of arrangement by the home country of applicant with America, usually done on a reciprocal agreement done by the two countries. Please ensure to leave sufficient time before travel for the loads of paperwork to be completed in case of applying for a permanent right to reside.