National Institute of Open Schooling has not yet released the date sheet for NIOS Class 12th exam. But it is expected that the theory exams may be conducted within October 3 to November 4, 2020. But this is an tentative date. No specific dates have been announced by the authority. Adding to this, This year there might be a delay in releasing the NIOS date sheet for October Exam as the situation is different this year and most of the events of 2020 have been delayed already. You should keep checking the official website for any furthur updates.