I think it's whatever the transaction date listed for the charge is, which would generally be based on the local time of the merchant. If you're thinking of any last big spending I wouldn't do it on July 30 or 31 though since there's occasionally a chance that a transaction date could come through later than the actual transaction for whatever reason (and for online spending many places will use a transaction date of when the purchase ships, not when it's ordered). For normal day-to-day spending you may have to settle with a couple of days of risking inefficient card use one way or the other...