It is 18:30, not 19:30 hrs. They did not communicate the change.
I have corrected it on my Sfakia website:https://www.sfakia-crete.com/sfakia-crete/ferries.html
You may need to reload that page in order to see the change.
You can watch the harbour webcam, to find out which ferryboat is going at that time:http://www.webcam-crete.com/
Have a good trip!
All the best,