Any possibility of a UNIX UTC timestamp field in the customer payment message?

For many transactions, the exact time of payment is when it is 'made' by the customer and not when 'requested' by the retailer or later mined. The blockchain time is an aggregate for the block and can differ significantly from transaction time so its value is limited.

Small slices of time can greatly impact the transaction value. If we are ultimately taxed as a currency, an exact time will for the transaction will impact US GAAP accounting and the transaction's tax accounting. A time field may also support 'first come first served' retailer programs and time sensitive promotions.