The Manual button is selected by default. When the manual button is selected, you will see the list of campaigns with the campaign name, campaign type, source, and action.

Under the actions option, you will see the date and time field. And you have to provide the date and time. On the time and date, the post will be published.

Just as you click on the date and time field, a calendar with the date and time will appear. From the calendar, select a date and time. In the manual settings, every post will be published on the specific date and time you have selected for the post. In the manual settings, every post will be posted only once.