How to Delay Trim Path "Start" Relative to Trace Path "Progress" in After Effects?

Hi everyone,

I'm working on an animation where a line follows a circle using Trim Paths in After Effects. The idea is to have the Trim Path "Start" property follow a Trace Path effect's "Progress" value, but with a 15-frame delay.

What I Have Done:

• I successfully linked the Trim Path "Start" to the Trace Path "Progress" using expressions:

   

  thisComp.layer("Trace Shape Layer 1: Path 1 [1.1]").effect("Trace Path")("Progress")

• However, I need a 15-frame delay before the Trim Path "Start" starts following the progress. That means when the circle moves for 15 frames, only then should the Start animation begin from 0.

Issue:

When I try using .valueAtTime() to introduce the delay, I get an error:
"Couldn't turn result into numeric value."

Question:

• How can I modify my expression to correctly introduce a 15-frame delay while ensuring "Start" follows the "Progress" animation smoothly?

• Is there a better approach to achieving this effect?

Any help would be greatly appreciated! Thanks in advance. 😊