To change your frame's Clock settings, please follow the below instructions:      

1. Go to the Frame’s Home Screen
2. Tap “Settings”
3. Tap “Date & Time” which will auto-adjust the date/time via your WiFi network
4. Select “24-Hour Format” to switch between regular and military time

If you see the clock and calendar when you frame is in slideshow mode, check out this article for help -How To Add or Remove the Time & Calendar from the Photo Display