Well... you can simply shift your time scale. Anyway your xlim is less than the range of t. If Dt is your translation (in your case Dt=2)
Instead of
plot(t,x);
use
plot(t-Dt,x);
Otherwise you can do the translation in the argument of your function.
x=(5/2)*(sign(t+2+Dt)-sign(t-2+Dt));
What's with the pause command at the end of your code?