The time will depend on the visa needed, and the mode of applying.In the case of non-immigrant visas, you must apply a minimum of 6 months in advance. If you belong to the immigrant category, you must apply between 3 and 9 months in advance. If your visa is for tourism or business, you can apply for an ESTA, which is the most straightforward way to apply. In this case, it is sufficient to apply online 48/72 hours in advance of travel. However, it is advisable to apply 15 days in advance in case of any problems that may arise.