freeat.php

<?php

$user = [
    "workHours" => [
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
        [],
        ["from" => "08:00:00", "to" => "16:00:00"],
    ],
    "sessions"  => [
        [
            "date" => "17/6/2017", "status" => "approved",
            "from" => "09:00:00", "end" => "11:00:00",
        ],
        [
            "date" => "17/6/2017", "status" => "new",
            "from" => "12:00:00", "end" => "02:00:00",
        ],
    ],
];

function freeAt($user,$newSession){ /* ... */ }