Did you know you can compare DateTime objects in PHP using the spaceship operator

test.php

<?php

$dates = [
	DateTime::createFromFormat('Y-m-d', '2000-02-01'),
	DateTime::createFromFormat('Y-m-d', '1994-01-30'),
	DateTime::createFromFormat('Y-m-d H:i:s', '2018-07-27 12:03:33'),
	DateTime::createFromFormat('Y-m-d', '2006-07-27'),
	DateTime::createFromFormat('Y-m-d H:i:s', '2018-07-27 12:04:15'),
];

usort($dates, function ($a, $b) {
	return $a <=> $b;
});