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Will I have entry/exit/visa issues if staying longer than 30 days as a US citizen?
Yes. DO NOT overstay your visa or you may not be allowed to return.
As a US passport holder, you get 30/20/10. On the 29th day, take the ferry to HK, pass through immigration, and then return to Macau (or stay a day). You will then receive 20 days upon your return.
If you go to HK before the 30 is up, it's luck of the draw when you return. For example, if you go on the 15th day, you may receive another 30 upon reenter. Most likely though, you would be stamped with the 20. That's why it's important to wait until the 30 is almost up.