Time is a measurement of what? How is it an illusion? Do you know what spacetime is? Movement is "real enough"?
Time is a measurement of change.
spacetime would be using the change of one thing (time) to measure the change in another (space). Movement is a change of space. Velocity, the rate of positional change relative to the change in whatever is being used to measure time.
I'd suspect to God, spacetime is as much of an illusion as is free will. To human beings, it's the reality of our perception.