The Final Hours
A full-time PhD could take about a thousand days from when you start work on your research to when you submit your thesis.
Getting ready for your viva is a modest chunk of work that could take twenty or thirty hours spread out over two to four weeks.
The viva itself might go by so fast that you’ll blink and miss it! Two, three, four hours? Maybe less, certainly not much more even for a “long” viva.
Thousands and thousands of hours of work to get to submission.
Twenty or thirty more to get ready.
Two or three to finally get the job done.
Those final hours matter, but rather than stress about what will, won’t or might happen in those few hours, it’s probably better to focus on the work you will have done in the thousands of hours before then.