Bettas arrived just fine. All are in their temporary tanks and swimming like crazy.
High today was 90+. Unfortunately, the USPS carrier (a sub; my regular carrier is great) put them in the black mailbox despite the many warnings on the box. The seller double-bagged and wrapped them in lots of paper which must have really protected them from the heat of the mailbox. I believe there may have been some Methyline (spel?) Blue in the water.
I added a drop of Prime to detoxify any ammonia as soon as I opened the bags. That's a trick I learned from Rachel at Inverts by Msjinkzd.