Which time format must be used when recording arrival and departure times on DHS Form 139?

When recording arrival and departure times on DHS Form 139, the 24-hour clock format is essential because it provides a clear and unambiguous way to represent time, particularly for official and legal documents. The 24-hour clock eliminates confusion that can arise from the 12-hour format, which uses "AM" and "PM" designations. In environments where precision is critical, such as security, law enforcement, or emergency response, this format ensures that times are easily understood by all personnel and minimizes the risk of misinterpretation.

The 24-hour clock is standard in military and official contexts because it allows for a seamless transition between hours without the need for additional clarifications associated with AM and PM. This is particularly useful for operations that span multiple time zones or require coordination among various agencies where clarity is paramount. By using the 24-hour clock, the records maintain a level of professionalism and adherence to universally accepted timekeeping practices in administrative forms.