添加一天到几小时

I have this:

$time = new DateTime('today 6 PM');
$now = new DateTime('now');
// check if current time is past 6 PM
if ($now > $time) {
     $time = new DateTime('Next Saturday 6 PM');
}

$diff = $time->diff($now);    
echo $diff->format("%h hours %i minutes remaining");

and want to add to the hours the days until the next Saturday, and that to every Saturday, so If we reach one it should automaticlly start itfrom beginning

You need to get each days, hours, and minutes separately:

$diff = $time->diff($now); 
$days = $diff->format("%a");
$hours = $diff->format("%h");
$minutes = $diff->format("%i");
$total_hours = $days * 24 + $hours; //figure out the total hours
echo "$total_hours hours $minutes minutes remaining";

 $plusSix = date('Y-m-d' , strtotime('+6 hours' , time())); // to add 6 hours

to check the day I think:

$dayNumber = date('w' , strtotime('2012-01-01'));