If you prefer 24-Hour Time, Sleep Pulse works with the system defaults of your iPhone or Apple Watch.
Visit Settings > General > Date & Time and turn ON the switch for 24-Hour Time.
Visit the Apple Watch Settings app on your iPhone. On the My Watch tab, scroll down and tap "Clock", then turn ON the switch for 24-Hour Time.
After toggling 24-Hour Time ON or OFF, restart the respective device to set the change so Sleep Pulse can properly analyze your sleep on the next use.