That's because hours are announced as points in time, while days are seen as time intervals. The duality intervals/separators is essential to the different ways

That's because hours are announced as points in time, while days are seen as time intervals. The duality intervals/separators is essential to the different ways to understand ranges (specially for range differences). I once developed a shortcut notation to simplify reasoning about ranges differentiating between "point cero" and "interval between 0 to 1", to make off-by-one errors less likely, but in the end it was functionally equivalent to the popular open/closed interval notations.