ACH settlement is getting faster. There's been a big push in the last few years, which will finish March 19, 2021 with three same day ACH settlement windows, and from what I can tell most (all?) ACH transactions under $100,000 eligible for same day settlement, with the remainder settling the at 8:30 AM Eastern the next business day (or future day if future dated).
What services banks and brokerages offer on top of that, can be more limited of course, but that's the state of the system.
I have seen a snail move through my garden at a faster pace. If it were 1992, and all we had were 9600kbps, then I could understand the burst all transactions after hours and then do the settle up over night. Suggesting that they are going to have 3 windows each day for settlement windows is a 1999 solution. That also sounds counter intuitive in that at each of those windows their systems will get slammed with orders to process. If they just let each one settle as they come in, then they would spread the load.
I'm really dumbfounded at how either I'm an idiot and just cannot understand the issue, or at how the rest of the world has been snowed over into believing it is terribly complex and takes decades to make incremental changes.
Not the rest of the world. Canada has fixed it. Interac settlement is 30 minutes max, with a $5000 limit, and interbank transfers are end-of-same-day. This is even assuming you have to change banks: there are only five banks, and they're regionally divided. Settlement in the same bank (and their investment arms!) is 30 minutes, even if the money is going to a different person. I paid for my house with this, and the payment was received before we walked out of the room!
It's only America's payment system that's woefully behind.
What services banks and brokerages offer on top of that, can be more limited of course, but that's the state of the system.