- var_dump: documentation ( source)
- preg_replace: documentation ( source)
<?php
$array_string = 'Array ( [0] => 2018-08-21 10:00:00 [1] => 2018-08-28 10:00:00 [2] => 2018-09-04 10:00:00 [3] => 2018-09-11 10:00:00 [4] => 2018-09-18 10:00:00 )';
$array_string = preg_replace('/\[(\d+)\] => (.*?)(?=\s+[[)])/s', "'$1' => '$2',", $array_string);
eval("\$array1 = $array_string;");
var_dump($array1);