Help with delaying tracking points

I've tracked the eyes of a subject and I'd like to create a light trail sort of effect, I have a plugin that creates the effect I want but needs me to track the start and end points. I've connected my start points to the track that I have but I need help connecting my end points in a way that follows my track but delayed by X frames/seconds (preferably something that I can keyframe so that it changes the length of the light trial during the shot)

Cheers!

To clarify this is in Fusion