BusyCal displays dates and times based on the format you have specified in System Preferences. It should work with all standard formats but may not always work with custom formats. To set a standard date and time format, open System Preferences > Language & Text > Formats, and select one of the regions from the Region menu.
If you wish to display times in a non-standard format, such as 24-hour time, you'll have to customize the time format as described in the following article.
http://www.macworld.com/article/132049/2008/02/ical24hr.html