The letter should include specific details like your relationship with the visitor, the purpose of their visit, duration of stay, and financial arrangements. What should the letter say?Because the visa application process may take 90 days or longer, we ask that you request your letters of invitation at least 90 days prior to your travel dates. There is no requirement for an invitation letter. If you want to send on send it to your parents who in turn may present it to the US consulate. Complete an Affidavit of Financial Support. Select your visa type: Determine the type of visa required to travel to the United States.