I did read that mates rates, the way you worded it made it difficult for me to find, I don't interperate it as you do otherwise we would be carrying alternates and tempo/inter fuel almost everyday, it's just a waffle on saying the times they give are the "most probable for the time of the forecast" with TS if you're going to arrive an hr before or after commen sense would tell you to take the gas, 12hrs before arrival would you carry the extra gas?!
"The specific value of any of the meteorological elements given in a forecast shall be understood to vary due to the limitations of forecasting techniques and limitations caused by the definition of some of the elements. The recipient shall understand that any specific element in a forecast will be the most probable value which the element is likely to assume during the period of the fore-cast. Similarly, when the time of occurrence or change of an element is given in a forecast, this time shall be understood to be the most probable time which is likely during the period of the fore-cast"