Met Office Climate stations, COl and lots of others use the 0900 z - 0900 z timeline to work out temp max and min , rainfall, gust etc, following advice in the Observers handbook. I try and follow the advice in there. I believe that our friends down under also use the same system. perhaps HairyMcLeary can confirm that. Not sure about the guys in the US though. It has been a Met Office standard for decades. Perhaps it is not a great thing,just be a lot easier for comparisons again my manual instruments here. It is in effect a global reset. It does cause some problems at end of month sometimes but rarely. It is understood that the 0900z refers to the previous day in terms of weather but is recorded against that day for statistical purposes. There are some guidance on that if you would like me to send it on.
If it is easy to do fair enough but if it is not it will not stop me using the program.
Best wishes
Mike