php strtotime time zone problem, in some years the UTC time zone and the PRC time zone differ by 9 hours

$timeStr='1987-5-4';
echo '测试时间：'.$timeStr;
echo PHP_EOL;
$prcTime=strtotime($timeStr);
echo 'PRC时间:';
echo $prcTime;
echo PHP_EOL;
date_default_timezone_set('UTC');
$utcTime=strtotime($timeStr);
echo 'UTC时间：';
echo $utcTime;
echo PHP_EOL;
echo 'UTC与PRC时间相差：'.(($utcTime-$prcTime)/3600).'小时';
echo PHP_EOL;

Result:

Test time: 1987-5-4

PRC time:547052400

UTC time: 547084800

UTC and PRC time Difference: 9 hours

After testing, the difference between UTC and PRC time for dates from 1987 to 1991 is 9 hours.

The php version is

PHP 7.1.9 (cli) (built: Aug 30 2017 18:34:46) (ZTS MSVC14 (Visual C 2015) x64)

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