You welcome. As noted I reply very frequently in these communities. I do so to help others and provide accurate information. Over the years I’ve worked with banks and for banks and other financial institutions (brokerages and insurance companies). My mother worked for the Federal Reserve Bank in Cleveland for a number of years. I know how the system works.
A one of experiment of transferring funds is not a test and other community members shouldn’t be tempted to draw conclusions. Size of the transfer is not a determining factor in when a transfer is completed.
Here is a good primer on ACH transfers.
https://www.nerdwallet.com/article/banking/ach-transfers
As noted in the article, ACH transfers only happen 7 times a day. Mid size and smaller banks may only transfer once or twice a day. Miss the transfer time and there are no 12 hour transfers.
Banks don’t publish when they transfer and banks are known to hold transfers for up to 24 hours or once per day. Miss a Friday transfer and nothing happens until Monday. Why hold transfers? To reduce costs to the bank. ACH transfers may be free for the sender and receiver, but not for the bank.
I hope this benefits you and other community members that come here looking for answers.