How do I apply a compositing node (for example "blur") periodically just for a part of my video?

I’m planning to apply a glitch and blur effect on various parts of a video using Blender 2.8 compositor nodes.
But I don’t know how to apply nodes to just specific frames of a video. I’d like to disable and enable in various parts of my video. What’s the easiest way?. Please help! : )