So, two things on this one, first, it looks like the screeps backend-local module hasn't been merged to master and published yet, so
system.setTickDuration doesn't exist in the CLI. Second,
screepsmod-admin-utils has the wrong help text in it, I'll poke at it tomorrow and fix that text.
As a workaround, for now, you can force an older version of screepsmod-admin-utils to get the tick rate function back.
screeps-launcher just add this to your
config.yml (keep it in the mods list too)
extraPackages: screepsmod-admin-utils: '^1.13.0'
or if using npm directly:
npm install --save screepsmod-admin-utils@^1.13.0