$re = '/([{,])(\s+)?(\w+)(\s+)?:/mi';
$str = '[{ endTime:"2019-06-05T17:15:00.000+10:00", startTime:"2019-06-05T17:00:00.000+10:00"}]
[{endTime:"2019-06-05T17:15:00.000+10:00",startTime:"2019-06-05T17:00:00.000+10:00"}]';
$subst = "$1\"$3\":";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php