You're merging date information into your email design. The default format includes the time stamp, so you need to change the display format.
- Click on Contacts and choose Configuration from the left-hand navigation
- Click on 'Custom Fields'
- Click 'Edit' next to the date demographic field being used
- Choose date display format from the 'Show dates in this format' drop down
- Choose 'do not display time' from the 'Show times in this format' drop down