It’s helpful to be kind to yourself and generous with timing for your viva prep. Getting ready doesn’t have to take long, but it won’t be the only thing you have going on.
When it’s time to plan your prep, spread the work out as much as you can. Something else may come along and disrupt your plans. Leaving yourself wiggle room gives you room to breathe, room to reshape your plans, space to not stress.
That wiggle room can always be used to rest if things do go according to plan!