Comment by silotis

These days ACH settlement runs multiple times a day. The biggest source of delay for ACH transfers is your bank delaying release of the funds for risk management. ACH transfers can be reversed even after they have "settled" and if the receiving bank has already disbursed the funds then they have to eat the cost of reimbursing the sender. Reversals are more likely to happen soon after the transfer completes, so delaying release of the funds makes it less likely the bank will be left holding the bag.