That’s the key to getting viva preparations done. There are core tasks and activities, but no blueprint for when, where and how you do them.
You need to read your thesis. Do you do that in an afternoon? For an hour per day? A chapter per night? You have to find your way to read your thesis.
You also need to annotate your thesis, make summaries, check papers, rehearse and build confidence. How do you organise yourself to do all of that?
You can go with the flow. You can make a plan. You can do it all in a week (probably not ideal!) or plot it out over a month or so. You have to find your way.
Much like the rest of your PhD journey, there are lots of ideas and guidelines, good advice and practical tips. Then you have to apply them to your situation, your circumstances.
You have to find your way.