I put down 6 months This is my mom's 2nd time. Last time she was only here for 1 month and returned on time. If you don't feel confident to put down 6 months, you can just put down 3 months. They will issue you visa for 1 year and multi-entry anyways. The customs officer will NOT see your visa application and you can still ask for 6 months when you enter the States.