How to animate boxblur radius in ffmpeg?

I am running the following ffmpeg command which converts a single image to a 10 second slow-zoom into the center of the photo.

As you can see, I currently have the boxblur looking how I would like it, but it is applied to the entire 10 second clip. I'd like to blur the first 3 seconds, and then animate the radius of the blur from it's current value of boxblur=10:9 to boxblur=0:0 from 3.0 - 4.0 seconds (24 frames at 24p).

Any help on how to achieve this?

ffmpeg -loop 1 -framerate 24 -i image.jpg -vf "boxblur=10:9,zoompan=z='min(zoom+0.0005,1.12)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=240:s=hd1080:fps=24" -c:v libx264 -pix_fmt yuv420p -t 10 -s hd1080 -crf 20  video.mp4

Recent Questions...