You can schedule unsent cards to be delivered on a later date from the "Send" step. Before sending cards, you will need to first build your mailing list. If you have not yet created your mailing list, here are directions on adding new contacts.

How to Schedule Card Sending

Step 1: Click the “Send” step.
 
Step 2: Click the "Schedule Send" send link.
 
Step 3: Review your envelope preview/s and scroll to the bottom of the pop up to select the date and time frame for the scheduled send.

IMPORTANT: All unsent contacts will be sent the card, even additional contacts added between scheduling the send and the actual send time.