Because it takes time to get from one point to another?
Usually it is considered the 4th dimension, since there are 3 spatial dimensions.
It also takes time when you don't move. Dimension means that one cannot be converted into another. You could replace time by velocity (preferably that of light in a vacuum), but you cannot replace length by time or vice versa.
Basically, yes. We can hypothetically set up a coordinate system where three of the axes represent locations in space and an additional axis represents a "location" in time. That gives rise to the notion of the interval, the separation in both space and time, which unlike spatial separation is not observed to be different by observers with different velocities.
How can there be time with no movement? There's nothing to measure?
Your heartbeat measures time. An atomic clock measures time, and it doesn't move at all (relative to the earth's surface).
Why isn't this preferred?
not measuring but confirming
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