Creating a particle system explosion without a collision
If you want to use a physics simulation, your best bet is to have a collision but don't render the object that collides.  I haven't used 3DSMax personally in a number of years, but there should be an option to have the object physically impact the scene but not be rendered by the render engine itself.  Then you simply do the collision to occur at frame 450 and it should behave the way you want as it does in the tutorial you are following.