This is a LIFE SAFETY issue so important that just the RISK of an »AM|PM« mixup is enough to use 24-hour time.
I believe that the 'a.m.' and 'p.m.' conventions should be abandoned. — Ross
I understand that some people are resistant to using 24-hour time, but please, if you still want to (or have to) designate a time using the 12-hour system, at least add AM or PM to it, so there is less confusion. For instance, if you tell people to show up at 8:00 on Saturday, some will show up in the morning and the rest will show up in the evening.