Nightbot does not stay in inactive channels on YouTube. To be classified as active, your stream must be live. While you can force Nightbot to join an offline channel by parting and rejoining it, it will leave as soon as the chat becomes inactive if the stream is not live.
As for a “bigger” command not showing up, you may be trying to post a message larger than what YouTube will allow. Off the top of my head I do not remember the exact limit, but it is probably in the 200-250 character range. We allow up to 500 characters in the Nightbot response, which accounts for the Twitch maximum.