Let us use the Matlab code on the Wikipedia Lorenz system page as an example:
https://en.wikipedia.org/wiki/Lorenz_system
Running this code gives you a vector t and a result matrix a. You can plot a for times greater than 50 only, by:
iplot = find(t>50);
plot3(a(iplot,1),a(iplot,2),a(iplot,3));grid on
To see how the curve develops, you may also try comet3:
comet3(a(:,1),a(:,2),a(:,3))
