That can certainly be done. All you have to do is to replace the last map block by something like:

map {
    ($date, $magnitude) = (split',')[3,4];
    [$_, normalize($date), $magnitude]
}
[download]

Then you add a subroutine normalize which transforms your date-time string into a value (string or numerical) which has the same value for each "slot". For instance:

sub normalize {
    my $value = shift;
    my ($hours, $minutes, $seconds) = $value =~ m/(\d{2}):(\d{2}):(\d{
+2}\.\d{3})$/;
    return int((1000 * $seconds + $minutes * 60 + $hours * 3600)/300);
}
[download]

As we now get a numeric result and not a string, we also have to replace the cmp in the sort block by a <=> to have the sort work correctly.

With a little effort you can further parametrize the subroutine so you can define the "slot" in a more flexible way without having to rewrite the sub every time.