Unless there is a compelling reason not to, the principal applicant and all derivatives should file their I-485 applications at the same time. If a derivative chooses not to file at the same time as the principal applicant, he/she may file Form I-485 up to six months after the principal applicant is granted permanent resident status. After six months, the derivative must file for following-to-join benefits via Form I-824, Application for Action on an Approved Application.