The default time setting for Omnia 2 is the 12 hours format. you can actually change to a 24HR time format for your Omnia 2. The instruction vary depending on whether your Omnia is running the Touch Wizard UI or Window Mobile.
In TouchWizUI
Goto Productivity --> Settings --> Advanced Settings --> System --> Regional Settings
Goto Time Tab. In Time Style, select HH:mm:ss
Goto Start --> Settings
Under System Tab --> Regional Settings..
Goto Time Tab. In Time Style, select HH:mm:ss
