You can monitor the PathFollow2D for that information. The
offset is the distance along the path.
if(pathfollow.offset > MIN_SHOOT_DIST)
Or if you know the normalized value you like, the
unit_offset could be used in place of that.
If you're looking for an X, Y position, you can grab the PathFollow2D's
global_position, and check if that's within an area or range that satisfies the goals of the AI.