Earlier quoted context omitted.
There's same day ACH, but I have no idea how widespread it is yet: https://www.nacha.org/same-day-ach-resource-center Anecdotally, I recently moved my banking to a discount broker and my paycheck is now credited to my account the night before. I don't know if that has anything to do with same-day ACH. Also anecdotally, Ally takes 5 business days (!) to open a CD via ACH even for an already verified bank. Definitely f…
Businesses use ACH extensively to pay each other same-day (and debit consumer bank accounts). But it has never caught on for consumer "push" payments.
That means for consumer accounts there's a ton more risk of things going sideways well after the money has moved on.
(Source: possibly outdated circa 2011 NACHA rules and transaction types)