That is a suggestion for optimum snail-mail delivery if you are from one of the 36 states that require it. Send the completed ballot back as quickly as you can.
Here is a good overview from the state department that may answer your questions:
https://travel.state.gov/content/travel/en/international-travel/while-abroad/voting.html
Pete, you are asking questions nobody is qualified to answer. Just hang on the that half until you return and let us know what happen then! Its a system in change.
According to 5his article, there were 2 earthquakes within seconds of each other. 6.8 followed by 7.7, after shocks were later:
https://mexiconewsdaily.com/news/7-4-magnitude-quake-felt-in-several-states/
... and then there is the Post from today (9/19/22) about an arrival at GDL Saturday 9/17.... No forms, just must recite your flight # (which of course EVERYONE knows for every flight they take!).