Some vivas are less than an hour in length. The shortest I’ve ever heard of was 42 minutes. This lead one participant at a Viva Survivor session to ask, “What can we do to make our vivas under an hour?”
The short answer: nothing.
The slightly longer answer: there are lots of factors in play that determine the eventual length of a viva. They range from the size of the thesis to the questions the examiners need to ask, and the way a candidate answers to the kinds of corrections that need to be considered. These all interact. It’s difficult to say what one could do for the best in order to reduce the length of the viva and still pass.
(of course, you could refuse to answer questions and your viva will be over very quickly…)
The better answer I should have given, by asking another question: why would you want your viva to be finished within an hour?