Long or Short
There are lots of reasons why a short viva might be “good” but no good reason to try and make it that way.
The viva is not a race, so you don’t have to rush. The viva is not a quick-fire quiz, so you don’t have to respond to questions quickly.
Listen.
Breathe.
Take your time.
Long or short, your viva will be over sooner than you think.