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.

if using screeps-launcher just add this to your config.yml (keep it in the mods list too)

extraPackages: screepsmod-admin-utils: '^1.13.0'