Nice having the babies, isn't it? Good for you!
I know some have reservations about fish being sent USPS, but it really wasn't that long ago that the US Mail was just about the only way it was done. (Well, not that long ago to me, anyway.)
Properly packed, 5 days or so is very easily possible. Not so expensive fish would typically be shipped with extras in the bag, to allow for a mortality or two, more expensive ones where shipped with fewer fish in the same size bag, to increase the survial rate. Less fish, more oxygen, fish tend to to very well.
We've been kind of spoiled with overnight shipping these days. (And I'm glad of it!)
Mike S.
Spring Hill, FL