An artificial space body began to move from the Earth with the third cosmic speed. How soon will it reach the stars?

The trajectory of this artificial body is a parabola. A body moving in a parabola at large distances from the Sun will have a velocity close to zero. The flight even to the nearest stars will take an extremely long time – millions or billions of years. Much more preferable is the hyperbolic orbit, in which the body, even at a very far distance from the Sun, will have a velocity different from zero.