#!/usr/bin/perl

my $start  = time();
my $sleep  = 600;
my $how_much = 5;
my $offset_file = '/tmp/offset.txt';
my $offset = 0;
print_to_file( $offset );

while ( 1 ) {
    sleep($sleep);
    my $now = time();
    if ( abs ( $start + $sleep - $now ) > $how_much ) {
        $offset = $start + $sleep - $now;
        print_to_file( $offset );
    }
    $start = time();
}

sub print_to_file {
    my $offset = shift;
    `echo $offset > $offset_file`;
}