One more hour of reading could help you to remember that key piece of information that’s slipped your mind.
One more conversation with your supervisor might boost your confidence for meeting your examiners in the viva.
One more look through your thesis with a highlighter in hand might show you that detail you’ve been missing – or the typo you’ve missed so far!
One more of any of these might be one too many things though: there is a practical limit of how much prep you can do and how much prep you need to do.
The viva is only one more day when you have to show up and do things you have done many, many times before.