My uni outlines 3 months as a guidance for time between submission and viva.

In reality, I was made to wait 9 months as my first examiner pulled out at the last minute and my university had to find a new examiner. Hand on heart, the most stressful experience ever.

Waiting time depends on examiners availability, obtaining examiners in the first place, any bank holidays/national holidays (ie Christmas, New Year, Summer Vacation) and to some extent if there are any problems with a thesis (in my case overly long thesis).

I'm currently working on my thesis corrections for PhD award.