I think that Time::Interval will be your baby ;-) You might want to keep http://search.cpan.org bookmarked.

/J\

 ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) = gmtime($sec);
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• $hours, $minutes, $seconds
• days as long as it's less than 365 (in $yday)
• years, if you subtract 70 from $year

Here's what I ended up using:

##
##  Convert an integer number of seconds into a 
##  formatted ddd:hh:mm:ss string.
##
sub s2d
{    
    use integer;

    my $s = shift;  
    return sprintf ":%02d", $s if $s < 60;

    my $m = $s / 60; $s = $s % 60;
    return sprintf "%02d:%02d", $m, $s if $m < 60;

    my $h = $m /  60; $m %= 60;
    return sprintf "%02d:%02d:%02d", $h, $m, $s if $h < 24;

    my $d = $h / 24; $h %= 24;
    return sprintf "%d:%02d:%02d:%02d", $d, $h, $m, $s;
}

##
##  Is year a leap year?
##
sub is_leap
{
    my ($yy);
    ($yy)=@_;

    if ($yy % 4 == 0 and ($yy % 100 != 0 or $yy % 1000 == 0)) {
        return 0;
    } else {
            return 1;
    }
}
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sub hms
 {
    my ($s) = shift;
    my ($h, $m);
    $m = int($s / 60);
    $s = $s % 60;
    $h = int($m / 60);
    $m = $m % 60;
    if ($s > 0) {
        $m++;
    }
    if ($m == 60) {
        $m=0;
        $h++;
    }
    sprintf("%s:%02d:%02d",comma($h),$m, %s);
}

# Convert a number to a standard english comma'd string.
# From "Programming Perl".

sub comma
 {
   local ($_) = @_;
   1 while s/(.*\d)(\d\d\d)/$1,$2/;
   $_;
 }
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