use strict;
use warnings;

my $expiry = time + 3600;

my $time = time;

sub sleepy {
  my $oldtime = pop;
  my $newtime = time;
  my $diff = $newtime - $oldtime;
  sleep 10 - $diff if $diff < 10;
  return 1;
}

while ( (sleepy $time)
        and $time + 300 < $expiry
      ) {
  $time = time;
  warn $time;
}