i suggest using dynamic key instead of static, and putting it on output gain in key tab, rather then moving the window itself. Set to be 1.0 in the last frame (or few frames before) you want the effect to be visible, 0 where you want it invisible, and back to 1 on the first frame you want it in full effect.
Film & Adverts Colorist, Media+ Belgrade
https://www.imdb.com/name/nm3829270/?ref_=fn_al_nm_1