If they file for divorce, it would be mutual, so that would take less time. However, for the divorce case to be accepted, the couple should be separated for over a year and be able to prove that they have not been able to live together, not necessarily in different ocations, but they haven't been acting as a married couple for that long. You cant file for divorce unless period of one year has elapsed from date of marriage except in exceptional circumstances. If they do file for a divorce before the first year, court will in most circumstances will wait 6 months to make the coupe reconsider their decision. This are the rules in India, unless I'm mistaken.
They can get an annulment on the basis that the marriage was was based on fraud or force considering Avni's real identity was concealed from the husband and family. Even then, there needs be substantial proof for this. As in, other than in cases of bigamy/polygamy or under age marriages, a marriage in India is rarely annulled.
I wish CVs didn't negate logic. Like they can use this information and craft a lot of good drama on the basis of it, and make it true to Neel's character, considering he most likely would already know about the rules and laws of India.