You don’t know how much time you’ll have in your viva. However long it is, it’s not worth stressing or obsessing. The best thing you can do is use the time that you have well.
Use your time to listen, pause and collect your thoughts.
Use your time to make notes if that will help.
Use your time to ask questions to clarify an examiner’s line of thinking.
Use your time to take a break.
Use your time to engage with the discussion, respond to questions and share your research.
Don’t focus on how long or short your viva might be. Instead, focus on how you can make the most of the opportunities you have in the viva.