Concept:
The Dayabhaga School of Hindu Law was formulated by the jurist Jimutavahana during the 12$^{\text{th}}$ Century. It became the principal school of Hindu law in Bengal and Assam.
Step 1: Recall the origin of the Dayabhaga School.
The Dayabhaga School was developed by Jimutavahana in the 12$^{\text{th}}$ century and differs from the Mitakshara School in matters relating to inheritance and succession.
Step 2: Analyse the options.
• 15$^{\text{th}}$ Century -- Incorrect.
• 12$^{\text{th}}$ Century -- Correct.
• 19$^{\text{th}}$ Century -- Incorrect.
• 9$^{\text{th}}$ Century -- Incorrect.
Step 3: Final conclusion.
Hence, the Dayabhaga School of Hindu Law was formulated in the
\[
\boxed{\text{12}^{\text{th}}\text{ Century}.}
\]