I am trying for a while now, but I have given up

Is there a way, in PHP, to use the current date and time and print / show the remaining hours to the same day every week.
Basically display a counting on a site in php (doesn't need to refresh automatically) which shows for example the remaining hours until Friday 5pm .. every week, so it automatically detects the day of the week and calculates the time automatically until the coming Friday.
All I can find so far is a way to calculate the remaining hours based on a date given in the script
$datestr="2014-03-28 17:00:00";//Your date
$date=strtotime($datestr);//Converted to a PHP date (a second count)
$diff=$date-time();//time returns current time in seconds
$days=floor($diff/(60*60*24));//seconds/minute*minutes/hour*hours/day)
$hours=round(($diff-$days*60*60*24)/(60*60));
echo "$days days $hours hours remain<br />";