In the assessment of risks of devices section (4.2) the standard lists duration of the risk as a parameter. This is an important distinguisher because it dictates how much damage a risk can do under worst case scenario. Oftentimes business decisions are guided by worst case scenario simulations. This metric tells you that, at worst case, a very severe and very frequent risk can only do damage for X amount of time. If this risk is a paralysis of the device but lasts for 0.1 seconds, it does not warrant much attention. By the time you diagnose and try to fix it its already over.