I remember knocking on my supervisor’s office door thirty minutes before my viva to check a mathematical definition.
I know of people who took the day off before their viva and just relaxed.
Some candidates will be checking notes almost until they go into the viva room.
It helps, as with writing the thesis, to decide in advance what you are going to do. Make a decision about what “enough” preparation looks like. What are the tasks you will complete? What needs to get done? I would suggest allowing for a little relaxation time the day before to relax your mind; perhaps you can make a special plan to do something nice, if your schedule allows?
You can stop when you’re done, and you get to decide when that is. Make that decision. Otherwise you may just keep nervously doing more and more until you start the viva.