Don't think there are any minimum. You can repay up to a maximum of 5 years.
You can get more details here: http://www.rhb.com.sg/personal/loans/reno_loan.html
For anyone who is interested, for the fix interest rate, the Effective Interest Rate (EIR):
1) For 3.22% is 6.21%
2) For 3.0% is 5.79%
As such, comparing with the variable rate, fixed rate of 3% is better.
Note: Interest is at all time low. Don't think it's recommended to take the variable rate - IMHO