Editing Animated Gif duration with GIMP

I made a screencast using Byzanz that went well, except that I had given it a duration that was perhaps 20 seconds too long.  The result was an animated GIF that needed to be truncated.

After a little research, I learned that you can do this with GIMP.

GIMP will import the GIF as a sequence of layers.  And each layer will have a duration as part of its name.  For me, I just had to delete the last layer, which was by far the longest in duration and the problem was solved.  Alternatively, you can edit the duration of the layer by editing its name.