I want to lengthen an animation containing one figure, and many props.  When I try to use the retime animation function, I'm only able to retime the figure.  Other objects in the scene, not associated with the figure, retain their original timing, which obviously doesn't work.  Am I missing something?

hi,

in order to lengthen the animation, just increase the max frame number (frame 1 to 30, change 30 into 300). This changes the upper limit for your frames.

Retime means that you want to rescale the animation, so your frame 10 becomes 100, 20 becomes 200 and 30 becomes 300. This slows down the animation as you stick with 30 fps or so. It;s a quite uncommon operation.
Usually, I build my animations at one key per 8 frames, so I can easily add intermediate at 4, then 2, then 1 frame distance. Then I find out that 8 frames take 1.8 second, so my original 8 frames go to 45 at 25 fps (PAL). I've got to do that with the main figuares in the scene far befor I've got that many props, or I really will have some job to do.

So, it's a per object operation indeed, and do not forget cameras and lights.