There's an interesting series of blog posts on the topic: https://engineering.gusto.com/how-ach-works-a-developer-perspective-part-1/ https://engineering.gusto.

There's an interesting series of blog posts on the topic: https://engineering.gusto.com/how-ach-works-a-developer-perspective-part-1/ https://engineering.gusto.com/how-ach-works-a-developer-pers... And the accompanying hackernews thread - https://news.ycombinator.com/item?id=7636066 https://news.ycombinator.com/item?id=7636066 But basically it seems like ACH is slow because the federal reserve runs once a day batches.