Hi,
Did you get an answer to your problem? I have been trying to do the same thing. Tried to use Basic Motion/Fade in-fade out on the Glow filter, but, it faded out the entire clip, even when highlighting (applying to) just the filter, it still faded out the video. I had to use keyframing, and it became more complex, and had to keyframe the threshold.
Cam
Cameron Young