gistfile1.php

<?php

// Rounds the given timestamp (string) up 15 minutes.
function round_timestamp($timestamp) {
  $interval = 15; // minutes
  $date_format = "%d-%b-%y %I:%M:%S %p %Z";
  $time_array = strptime(strftime($date_format, strtotime($timestamp)), $date_format);
  $minutes = $time_array['tm_min'];
  $delta = $minutes % $interval;
  $time_array['tm_min'] = $minutes + ($delta * ($delta < $interval / 2 ? -1 : 1));
  $new_timestamp = mktime($time_array['tm_hour'],
                          $time_array['tm_min'],
                          $time_array['tm_sec'],
                          $time_array['tm_mon'],
                          $time_array['tm_mday'],
                          $time_array['tm_year']);
  return strftime($date_format, $new_timestamp);
}

?>