Earth time and traveller time
At ordinary speeds, both are practically identical. Near light speed, special relativity predicts that less time passes aboard the moving ship than for observers who remain on Earth.
Science & speculation
Interstellar Travel Time Calculator
How long would another star take to reach—and how different would the journey feel aboard the ship?
What the calculator leaves out
Real missions must accelerate, decelerate, carry energy and shielding, survive radiation and navigate around hazards. This is a clean constant-speed comparison, not a mission design.
Communication cannot cheat
A signal travelling at light speed still needs one year to cross one light-year. An interstellar civilization may solve transport before it solves conversation.