I recently wanted to show the "up time" for a script in "nice" units. ApproxTime below is the result.

use warnings;
use strict;

printf "%9d seconds is about %s\n", $_, ApproxTime ($_)
    for 4, 250, 1.5e4, 4e5,  3e6, 12e6, 1.5e8;

sub ApproxTime {
    my ($period) = @_;
    my @periods = (
        ['seconds', 180,    60],
        ['minutes', 240,    60],
        ['hours',    48,    24],
        ['days',     16,     7],
        ['weeks',    10,     4.3482143],
        ['months',   30,    12],
        ['years'],
        );

    while ($periods[0][1] && $period > $periods[0][1]) {
        $period /= $periods[0][2];
        shift @periods;
    }

    $period = int $period;
    return "$period $periods[0][0]";
}
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Prints:

        4 seconds is about 4 seconds
      250 seconds is about 4 minutes
    15000 seconds is about 4 hours
   400000 seconds is about 4 days
  3000000 seconds is about 4 weeks
 12000000 seconds is about 4 months
150000000 seconds is about 4 years
[download]