This is a good place for a Schwartzian transform...

@r=qw( 1:00AM
  2:45PM
  8:30AM
  3:15PM
  6:15PM );

 @t=map { $_->[0] }
  sort { $a->[1] <=> $b->[1] }
  map { $a=$_;
        s/://;
        s/(\d+)(\w)M/$1+($2 eq "P"?1200:0)/e;
       [ $a, $_ ] } @r;

# @t has your sorted times.
[download]

The second map can be shortened up a bit. I'm just making what's going on there a little more obvious...