To schedule a promo campaign, simply follow these steps:
1. Select "Promotion -> Promotion Sender" from the top menu
2. Select your campaign or create a new campaign if necessary
3. Select the "Promo List" option
4. Next to the "Send When" option select "Scheduled"
5. The "Schedule" options will now appear so you then select "Add Promo List To Schedule" 
6. Select your promo list and enter all relevant information
(Please note that when scheduling a promo campaign, if you want to enter a custom message you need to do this on the Scheduler options and not in the Promo Sender Control Panel)
7. Click "Schedule" to save