How do I use terminal to change the desktop wallpaper folder and enable "change picture every minute" plus "random order"
Turns out https://stackoverflow.com/a/39208361/130638 is the magic.

Here is my completed script:

#!/usr/bin/env bash
source "$HOME/.scripts/sources/strict.bash"
# https://apple.stackexchange.com/a/326863/15131
# https://stackoverflow.com/a/39208361/130638

function wallpaper {
    path="/Users/balupton/Documents/Media/Media - Wallpapers/High Quality/Time/$1"
    osascript -e 'tell application "System Events" to tell current desktop to set pictures folder to "'"$path"'"'
}

if is-affirmative "${1:-}" "yes"; then
    echo 'enabling dark mode...'
    osascript -e 'tell application "System Events" to tell appearance preferences to set dark mode to true'
    wallpaper Night
elif is-affirmative "${1:-}" "no"; then
    echo 'disabling dark mode...'
    osascript -e 'tell application "System Events" to tell appearance preferences to set dark mode to false'
    wallpaper Day
else
    echo 'toggling dark mode...'
    osascript -e 'tell application "System Events" to tell appearance preferences to set dark mode to not dark mode'
    wallpaper Popping
fi