A simple delay question

Hi all,

I have three movie clips on the stage that I want to animate their alpha by using:
mc01.tween("_alpha",100,15,0,0);
mc02.tween("_alpha",100,15,0,0);
mc03.tween("_alpha",100,15,0,0);

Everything works well.

My question is how can I create a delay for each one: i.e mc01 appears and after 3 seconds disappears while mc02 appears, waiting for another 3 seconds and disappears while mc03 appears ans so on and so forth - all in one frame.

Thanks,
A.O