The First Day Of Viva Prep
It’s not the day you submit, or the day after.
It’s not the first time you read your thesis after submission, or when you start to get ready for a mock viva.
It isn’t even when you really start to plan for submission, or first think about what your examiners might ask.
The first day of viva prep was a long time ago. The first day of your PhD, whenever you started the work that has lead to your thesis. You have been preparing for a long time before you get to the viva: developing your talent, building your knowledge, getting better.
A little extra prep after submission is needed to be ready. Don’t forget though, for your confidence, that you have been preparing for a long time.