# Composite two scenes for only a short period?

I have a scene with a particle emitter and a second scene with the actual particles. I separated them so I could have more control over motion blur.

When I try to render the animation, it renders both scenes on every single frame, but the particles are only in the scene for a couple frames in the end.

So my question is: can I tell the compositor to render and combine two scenes for only a few frames at the end instead of rendering and combining both scenes for the entire clip? I imagine it would save render time.

You can add a Switch node in the compositor (Shift + A > Layout > Switch), and keyframe which input it uses by hovering over the checkbox and pressing I.