Sounds like “banker-speak”, but “Same Day ACH Debits” might have a surprising effect on your account if you are not aware of what will happen.
In the past, electronic deposits (ACH Credits) went into your account before the start of business each day and electronic withdrawals (ACH Debits) came out of your account at the end of our business day. Beginning in 2016, the banking system began processing “Same Day ACH Credits” which meant that electronic deposits to your account could be processed during the day, although most still come in very early in the morning. Starting on September 15th, ACH Debits will also be withdrawn from your account during the day.
If you writing a check to a store that converts it to an electronic item (because they want to get their money as soon as possible), that withdrawal could come out of your account before you have the time to drive to the credit union and make a deposit. If you authorize a credit card company to withdraw a payment from your account today, you can’t assume that it will take a day or more to show up on your account.