If the billing date is 20th and the repayment date is 6th, the money spent by swiping the card at 10 will enter the bill issued on 20th, so you need to pay back the money before 6th of next month. If you swipe your card at 2 1, it will enter the bill on the 20th of next month, and you can repay it before the 6th of next month.