Step 1: Information Retrieval.
The provided text explicitly states that the maximum repayment duration for Kisan Credit Cards is 12 months.
Step 2: Option Exclusion.
- 9 months: Inadequate duration.
- 24 months and 20 months: These periods are not specified within the scheme's guidelines.
Step 3: Determination.
Therefore, the maximum repayment period is 12 months.
Final Answer: \[\boxed{\text{Kisan Credit Card repayment period = 12 months.}}\]