Why do some businesses not accept American Express cards?
American Express transactions in particular cost merchants more to process than Mastercard or Visa transactions. This means that the merchant ends up losing more money on transactions with American Express cards than with other cards, so they may choose to refuse them.

What is time limits apply for Mastercard from transaction processing date?
Hi Valory,
Thank you for your inquiry.
We’d be happy to assist you further if you could confirm or clarify your question.
Thanks and cheers,
May