MindMixer does not offer a holding place or queue for topics to be published later. Topics can be put into draft form to be revised before publishing. You can also select a future date for a topic to post and it will deploy on the date you've established.
The front end of your MindMixer site will show site administrators drafted topics as they would appear if they were published but will not be viewable by participants until they are live.
Topics with a future start date can be viewed by participants in the Topics tab under "Coming Soon".