Ok, tried it again and used 12/31/2018 for both dates and it did work, and just in time 🙂 Thank you Ho1lst!

Also even when the entire 1099-DIV was deleted, the TurboTax Online Review still showed that the dates needed to be entered -

Thank you for your comment. It basically wants me to enter the types of information from a long term sale that would be reported on a brokers combined statement...