Dear aspirant

Yes, if you belong to OBC-NCl category,you can take benefit anytime you want. OBC-NCl candidate are those who is obc and his family income is below 8lakhs/annum. Then only you are eligible for taking benefits of it, otherwise besides belong to obc category but your addmission will happen through general category rank of you don't fulfill above mentioned criteria.

For taking benefits from start to end you will have to mention obc as your category that means from filling application form to participating counselling every where you should mention same category for an exam. To take benefit of it you will have to produce valid OBC-NCl certificate.

Hope this information helps you

All the best!!