hello aspirant,

You need the category certificate during the counselling and admission.so there would be no problem if you dont submit the ews category certificate now during the resgiration or application.it wont ask the hard copy  of the certificate but it asks during the jeeadvanced registration.so if you dont have the certiciate from central government i suggest you to apply as soon as possible before the admission takes place otherwise you will be considered as GEN student.

hope this helps,

thankyou.