Final Answer to this Q regarding AMEX Charge Cards
All AMEX Charge cards are 30 day accounts.
As long as AMEX receives payment in full on or before the closing date of your next billing cycle, your payment is on time. Period.
If you want to pay automatically each month, then the first month your bill is paid early. Which means you will not have the full 30 day grace period, but only for the first month you sign up for auto-pay. After that, you will still have the 30 day grace period because your auto-draft will happen the same time each month.
Always ignore the "Due Date" on AMEX charge cards. Make sure you know your "Closing Date" and follow that each month. If you get this wrong, then your payment will be late, and you will have violated your AMEX CC agreement.
Also, if you wait until the exact closing date to pay, and the website is down, or the phone system is down, you will still be in violation of your CC agreement, since the T&C excludes such technical issues as valid reasons for paying late.
PS - You do not have to wait an hour after you eat to go swimming. And always wear your seat belt.