#!/usr/bin/perl
use strict;
use warnings;

my $run_limit_hours = 9;              # You would of course grab this from @ARGV or something
my $start_time = time;                # Number of seconds since epoch
my $end_time =                        # Deadline -- end time in seconds-since-epoch
    $start_time +
    $run_limit_hours * 60 * 60;       # 60 seconds per minute, 60 minutes per hour

while (1)
{
    my $current_time = time;
    if ($current_time > $end_time)
    {
        last;
    }
    &doTheThing();
}

exit;