Om Sai Ram.
In my humble opinion, you can complete the parayanam today, that is on MahaShivratri. It is an auspicious day, and completing it today will be good. In fact, there are no rigid rules and regulations in Baba's path. He only needs our Shraddha and Saburi. If you complete the parayanam with full faith and devotion to Baba, He will accept it. Kindly forgive me if any Sai bandhu has objections to my opinion.
Wish you a happy Shivratri. May Baba bless all.
Om Sai Ram!