Check if date and hour / minute have already expired

I am having a problem, when uploading my website to PHP 5.6 the code I use to check if such date and such time / minute has expired is simply not respecting the time, if it is the date already speaks that expired without checking the hour / minute. Does anyone have a solution?

$sql = "SELECT * FROM noticias WHERE programada = 'sim'";
$res = mysql_query($sql) or die(mysql_error());
if(mysql_num_rows($res)>0){
$row = mysql_fetch_array($res);

function NoticiasProgramadas($data){
    $dt_expira = str_replace("/", "-", $data);
    $dateInicio = date('Y/m/d G:i:s', strtotime($dt_expira));
    $timestamp_dt_expira = strtotime($dt_expira);
    $dt_atual = date("Y/m/d G:i:s");
    $timestamp_dt_atual = strtotime($dt_atual);

        $ret = '';
        if ($timestamp_dt_atual >= $timestamp_dt_expira) {
            $ret = "exp";
        }
    return $ret;
}
$d = NoticiasProgramadas("$row[postdate] $row[posthora]");
if ($d == "exp"){

//executa um código mysql

}