well, uh, how about military time?
there's lots of good ways to do this. date::manip and all that. how about something less optimal, but wacky?

 
$_= "11:12AM";
tr/://d;
if (s/(\d\d)(\d\d?)([A|P])M/$1$2/) {
    if ($3 eq "P") {$_ +=1200 unless $1==12};
}
print $_;
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update Military Time ™ crazyinsomniac.