The Bridge of Preparation
You submit your thesis, you have your viva and in between these two events is the bridge of preparation.
Viva prep bridges the gap between one challenge and another, but the gap is not that great and the bridge is not so difficult to build. A little effort spread out over a few weeks can be enough to ensure that you get from submission to the viva with no problems.
Maybe you can leap the gap, but why leave it to chance?