Posterize Time Effect
"The 'Posterize Time' effect can be used to set a frame rate for
a piece of footage or a nested sequence. However, in this tutorial,
Andrew Devis shows how to use it as a special effect to create
dramatic looks for your footage or to give the impression that the
footage was taken on an older camera which worked at a different
(usually lower) frame rate. (Note: Although it is possible to animate
this effect, it can cause unpredictable results and so any keyframes
created will be hold key frames giving instant transitions rather
than gradual changes)."
Drop the footage into a new sequence and speed it up dramatically.
Then nest that sequence and slow it way down.
What that does is automatically cut out frames for you. Speeding it up drops them, and slowing them down means repeating frames.
Export timeline as a bmp sequence (or tiff or png)
Set framerate to e.g. 6 frames per second.
Now import all the stills and set the duration of the stills to e.g. 6 frames.