This method will guide you to change the time format in Outlook calendar and show all time labels as military time or 24-hour clock. Please do as follows: 1. Open the Control Panel with one of below ways: A. In Windows 10, please click the Search icon at task bar, type control panel into the search box, and then select the Control Panel in search results. See right screenshot: B. In Windows 8, press Win + S keys to activate the Search pane, type Control Panel into the Search box, and then click Control Panel in the search results. C. In Windows 7, Please click Start > Control Panel.

2. In the opening Control Panel, type Region into the search box right to the folder address box, and then click Region (or Region and Language) in the search results. See screenshot:

3. Now the Region dialog box comes out. Under the Formats tab, please (1) select HH:mm from Short time drop down list, (2) select HH:mm:ss from Long time drop down list, and (3) click the OK button. See screenshot:

Note: For changing to custom time format in Outlook calendar, please (1) click the Additional settings button in the Region dialog box; (2) in the Customize Format dialog box, enable Time tab, (3) type time format codes into both Short time and Long time boxes, and (4) click OK buttons to save the changes. See screenshot:

After configuring the time format in the control Panel and returning to Outlook calendar, you will see the time labels are changed to military time (24-hour clock) as below screenshot shown.

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