I have just received my Base Club Vistara Credit card today. I am hoping that I will receive my complimentary flight voucher by latest 15 days after the 2nd bill generation date. Maybe SBI waits for 2nd bill generation to ensure we have paid our 1st card bill before due date and no finance charges have been levied. Then sends the flight voucher within the next 15 days. But I am not sure. I will wait till my assumed deadline.