If you are covered under ESI, you will get the benefits of the scheme, otherwise you will get the benefits under the Maternity Benefit Act (amended as in 2017). Either way, the amendment in 2017 has increased the period of paid maternity leave from 12 weeks to 26 weeks.
Previously, out of the twelve weeks, up to a maximum of 6 weeks could be taken before the date of delivery and the remaining after delivery.
Now, the maximum period of leave before expected date of delivery is 8 weeks and the remaining up to a total of 26 weeks (including the leave taken before delivery) can be taken after delivery.
In your case, since you have probably not availed any maternity leave before the date of delivery as it was preterm, you can avail full 26 weeks paid leave from the date of delivery. Following your delivery, you have to take leave to regain your full health, as Mr. Madhu has so rightly said. Also, during this time, you may have to attend to the baby in the Hospital where the baby is admitted. That is also part of caring for the baby. So don't think about going to work now and taking maternity leave later. In any case, maternity leave starts from the date of delivery, and not from any other date.
If needed, you can extend your maternity leave beyond 26 weeks also. There is a provision for that in the Maternity Benefit Act.