Imagine you are operating a temperature station in July, 1936 – the hottest month in US history. Your time of observation is 5 pm. The temperature is 109 degrees, and you reset your thermometer.
At 6 pm, a cold front comes through and the temperature drops to 60 degrees. The next day is 40 degrees cooler, but your min/max thermometer reads a maximum of 109 degrees, from when you reset it a day earlier. Are you actually going to enter 109 degrees for the high that day?
Of course not. Any responsible person will reset their thermometer at night, regardless of the time of observation. TOBS is not a subtle problem. It is a very much in your face problem as the station operator, and I have a very hard time believing that many people would be irresponsible enough to reset their thermometer at 5:00PM, and then not reset it again until the next afternoon. It doesn’t pass the sniff test of human psychology.