Otherwise I wouldn't have written it down. Time in the physical sense is always relative and never absolute. That's just a cultural fixed point. When the aliens land on Mount Shasta they'll have a different chronometer reading in their spaceships, using different units and a different zero point. This idea of local time is not what we mean when we talk about time in physics.
Time is a cultural construct whereby an event can be associated with a series of numbers.
Well let me tell you right now that nobody ever gained an hour when Daylight Savings Time ended, not literally anyway. Time in the former sense, as used in physics, is measured with a stopwatch or an interval timer, while time in the latter sense is determined with a wristwatch or clock. In the course of your study of physics you'll have to understand the difference between the two meanings of this one word. The exact definition of mean solar day was based on astronomical theories. However, measurement showed that irregularities in the rotation of the Earth could not be taken into account by the theory and have the effect that this definition does not allow the required accuracy to be achieved.