Checking the time while you’re in the viva won’t help.
Most vivas, based on all the conversations I’ve had over the last decade, seem to be in the two- to three-hour range. That knowledge can help you to prepare a little, think about how rested you need to be and what you might need to be ready to talk for that long. But it won’t help you in the viva to look at a clock and know that an hour has passed.
There’s no correlation between viva length and outcome. Looking at the time will only make you wonder. “How am I doing?” or “Two hours already?!” or “This is going fast… Is that good?!”
Have an idea about how long the viva could be to help you prepare. Turn your mind away from time when you’re in there. Pause, take time to think and respond. Don’t rush, don’t worry.
It will probably be over sooner than you think, and only take as long as it needs to. You are going to be fine however long it is.