how to add object to a keyframe range? lets assume we have an iron man pointing his hand to a target and shooting few frames later as shown in the picture below:



frame 0 to 10 he will point frame 11 to 15 he will shoot, which is just a long cube with one larger face to give idea or a laser projectile 

how can I add the projectile cube only on frame 11?
I don't what it to exist before that

thanks
You could keyframe the visibility and the renderability of the shot object in the outliner (RMB over the icons and insert keyframe:




Disable visibility and renderability in frame 0 and add keyframe
Enable in frame 11 and add keyframe