Hi @goodgoblin!
As you suggested, controlling the fps works fine:
> ~/Downloads/dmengine_headless --config=display.update_frequency=10
However, this is probably not what you wanted to achieve, since the game is essentially still running as fast as possible, with that new (fixed) time step.
And, unfortunately, there doesn’t seem to be a proper sleep function in lua, but there are some alternatives here (quick google). Perhaps one of them could work, depending on your requirements.