This is really interesting... I currently use and administer our Intuit Online Payroll account. I'm required to run payroll only 2 full business days before pay day. Does the final credit stage you mention here not introduce any additional delay? (Read: is IOP doing the same thing to their main account?)

Also, are you or IOP able to collect interest on the 3 day float? Or does interest not accrue for not fully guaranteed funds?

Finally, is the clearinghouse account you utilize internally not something of a high-risk target? I understand there are safeguards in place to prevent unauthorized false requests, but the thought of even temporarily acting as a go between with somebody else's funds like that feels an awful lot like being a bank without the rewards.