Hello there!

Greetings!

Yes dear you can appear in NIOS  exam after completing your class 12th exam in 2019 from regular board like cbse or any state board etc . But for that you don't need to wait for 1 year , I mean you do not need to wait and give Nios exam in 2020 rather NIOS exam is on demand.  Anyone having  secondary education certificate i.e. class 10 th certificates  are eligible to given exams for senior secondary (class xii) exams. So , you will be eligible even after passing 12th from regular board.
Thankyou