Extracting the pertinent parts of your code we see this:

sub log_watch {
...
    my $timestamp = 0;
...
        if ( $line =~ m/^(\d+\/\d+\/\d+\s\d+\:\d+\:\d+\.\d+)/msx ) {
            $timestamp = $1;
        }
...
    return $timestamp;
}
[download]

From which we can conclude that as $timestamp is still zero at the return point, your regex does not ever match $line. So, either your regex is wrong or $line is not what you think it is, or your log_watch method returns before $line is even tested or you have no entries in $self->{'stdout'}.