From my knowledge, I don\'t think it delays the process of the primary applicant in any way, if the dependent\'s case was filed before the primary\'s case was adjudicated. The fact that the dependents case will be attached to the Primary\'s case gives the leverage that both might be processed same time. But the chance that primary\'s Fp is already done, then primary get approved and dependent might be under process. I have not seen any postings so far depecting your question. Again this is my thought process.
