$data = [
    (object) ['myDate' => '2017-01-12'],
    (object) ['myDate' => '2016-12-25'],
    (object) ['myDate' => '2017-01-01'],
];

function dateSort($a, $b) {
    return $a->myDate <=> $b->myDate;
}

usort($data, 'dateSort');
var_dump($data);

$data = [
    (object) ['myDate' => '2017-01-12'],
    (object) ['myDate' => '2016-12-25'],
    (object) ['myDate' => '2017-01-01'],
];

function dateSort($a, $b) {
    return $a->myDate <=> $b->myDate;
}

usort($data, function($a, $b) { return $a->myDate <=> $b->myDate; });
var_dump($data);

$data = [
    (object) ['myDate' => '2017-01-12'],
    (object) ['myDate' => '2016-12-25'],
    (object) ['myDate' => '2017-01-01'],
];

function dateSort($a, $b) {
    return abs(strtotime('2016-12-31') - strtotime($a->myDate)) <=> abs(strtotime('2016-12-31') - strtotime($b->myDate));
}

usort($data, 'dateSort');
var_dump($data);

$data = [
    (object) ['myDate' => '2017-01-12'],
    (object) ['myDate' => '2016-12-25'],
    (object) ['myDate' => '2017-01-01'],
];


$pivotDate = '2017-01-06';
usort(
    $data,
    function ($a, $b) use ($pivotDate){
        return abs(strtotime($pivotDate) - strtotime($a->myDate)) <=> abs(strtotime($pivotDate) - strtotime($b->myDate));
});
var_dump($data);