The answer to most of these concerns is quite simply read the Sous Vide Bible:
It explains pasteurisation. It gives you tables for the temperatures and how long to achieve pasteurisation for a given thickness of meat or poultry at any given temperature.
Times for pasteurisation are in addition to the time to reach temperature equilibrium (when the core of product cooking has reached the same temperature as the bath) which can be roughly calculated by one hour per inch of thickness.
Still worried? Invest in a quality instant read digital thermometer.
The variation in the times given has been covered many times on this forum. Here’s just one of them: