I got that advice a lot during my PhD. “It’s a marathon, not a sprint.” I had to pace myself for the long journey to success.
The viva’s not a sprint but it’s also not a marathon either. It’s not a race of any kind, you’re not being tested on how fast you answer but on how well you answer.
Don’t rush. Rushing to answer a question isn’t going to help you, your thesis or your research.
Pause. Breathe. It’s not a race, but the end of your journey is near.