I agree that you have a very narrow window with the Starwood Amex. I got around this by using the pay by phone option that withdraws any amount I want each month from my checking account, that I preregistered with Amex. I still pay at least 48 hours before the payment is due to be on the safe side. And be warned, when you call to pay by phone the amount that will be "read" to you will be your current balance which will include recent charges that won't be due until the end of the next billing cycle, so have your current statement handy when you call to pay.