Interviewer - Server > Configuration and customization > Web configuration files > Settings for the Phone Participants activity > Enabling the 24-hour clock
 
Enabling the 24-hour clock
The UseTwelveHourClock key specifies whether the 12-hour or 24-hour clock is used. When set to false, the 24-hour clock is used and the AM and PM indicators are hidden. The 12-hour clock is used when the setting is not defined.
<appSettings>
  <add key="UseTwelveHourClock" value="false" />
</appSettings>
See also
Settings for the Phone Participants activity