Go to Settings -> Report Settings to indicate your preference for 12 hour (AM/PM) or 24 hour times in reports.
Date and time format settings are located in the product's registry key. The values are all named DateFormat_xxx.
Each product's registry key is shown below, along with a link to a small registry file that will set times to 24 hour format for you.
Note that the registry file is currently set to .txt -- you will need to save the file and rename to .reg before importing into the registry.