...
my $stop_time = time + 60 * 60 * 7; # now + 7 hours
while (1) {
    do_work;
    last if time > $stop_time;
}
...

##</code><code>##

...
while (1) {
  do_work;
  if (-f '/tmp/script.die.die.die') {
    unlink '/tmp/script.die.die.die';
    last;
}
...