Originally Posted by
washeelers747
Agreed. Probably not best source but TPG post indicated that it's fine to use same negative test for U.S. bound flight if it's less than 72 hours. Probably useful for U.S.-South America mileage running if someone feel comfortable to do it. Here's the answer on post.
"What if I’m gone for less than three days?
If you get a negative test, travel and return within three days, the test before departing the U.S. will be accepted.
Brazil requires a PCR test, so unless you're one of the lucky people who live in an area where you can get a rapid PCR/NAAT test, you are most likely going to take your test for Brazil more than 24 hours prior to leaving for Brazil. That means the 48 hours added to the lead time for the outbound test probably puts the traveler beyond the 3 calendar days. That said, if it's a rapid turn-around like 48 hours, take a rapid antigen test before leaving the US. That will be acceptable to getting back to the US.