Hi there, @nathan-hall-sd.
Thank you for visiting us today. I can share some information about the pop-up message when creating a transaction before the closing date.
Close the Books feature allows you to keep track and prevent other users from making any changes to the prior accounting period.
Once this is turned on, transactions dated on or before the set date will receive a pop-up message. This is to notify you that the transaction will affect your account balances.
That should be enough information to answer your question.
Don't hesitate to add a comment if you have additional questions. I'd be happy to help. Remember I'm here cheering for your continued success.