Round minute down to nearest quarter hour

This code is enough for get the solution,

function roundToQuarterHour($timestring) {
    $minutes = date('i', strtotime($timestring));
    return $minutes - ($minutes % 15);
}

The solution is very simple,

$seconds = time();
$rounded_seconds = round($seconds / (15 * 60)) * (15 * 60);
 
echo "Original: " . date('H:i', $seconds) . "\n";
echo "Rounded: " . date('H:i', $rounded_seconds) . "\n";

The code above can be used for both original and rounded value.

We can also use floor() function instead of round() which is used for round it down.

Try to use this code,

$now = getdate();
$minutes = $now['minutes'] - $now['minutes']%15;
 
  //Can add this to go to the nearest 15min interval (up or down)
  $rmin = $now['minutes']%15;
  if ($rmin > 7){
    $minutes = $now['minutes'] + (15-$rmin);
  }else{
      $minutes = $now['minutes'] - $rmin;
  }
 
$rounded = $now['hours'].":".$minutes;
echo $rounded;