Why does Excel treat time as nothing but the time of the day, starting from year 1900?

If I have a pencil that is ten inches long, it is not as if one end of the pencil is so many miles, so many furlongs, so many yards, so many feet, and so many inches from the center of the earth, and the other end of the pencil is that much plus ten inches from the center of the earth.

I have great difficulty in getting Excel to consider values of time intervals, such as time to complete a task, response time after a stimulus is noticed, time taken to walk a mile, or complete formatting of a document. Why should all these intervals of time have to be tied up with time of the day concept? Sure, I have devised various ways of working around this limitation of Excel, but every time I do, I am surprised as the lack of a time duration variable.

Why didn't the programmers at Microsoft ever consider designating a simple time variable, divorced from a time-of-the-day variable?