$wp_time = current_time( 'timestamp', 0 );
$chat_time = get_field('chat_time', 'option');
$chat_time_from = array();
$chat_time_till = array();
foreach($chat_time as $ct) {
    $chat_time_from = strtotime($ct['chat_time_from']);
    $chat_time_till = strtotime($ct['chat_time_till']);
    if ($wp_time >= $chat_time_from && $wp_time <= $chat_time_till) {
        echo "show";
    } else {
        echo "dont";
    }
}