There is is only an options for "One" when you edit the Language under Checkout & system and USPS Priority Mail Express and USP Overnight Air are considered one day when USPS Priority Mail Express is actually a 1 - 2 business day. I need to separate these two out so I don't have this issue below with USPS Priority Mail Express and UPS Overnight Air overlapping like this. Help me out here.
You can use the Multi Carrier Shipping label app and separately show USPS Priority Mail express as well UPS Overnight options with the delivery estimates at checkout. I hope i understood your problem correctly.