function RandomQuoteByInterval($TimeBase, $QuotesArray){
  // Make sure it is a integer
  $TimeBase = intval($TimeBase);
  // How many items are in the array?
  $ItemCount = count($QuotesArray);
  // By using the modulus operator we get a pseudo
  // random index position that is between zero and the
  // maximal value (ItemCount)
  $RandomIndexPos = ($TimeBase % $ItemCount);
  // Now return the random array element
  return $QuotesArray[$RandomIndexPos];
}
/*
** --> See the example section below for a
**   detailed instruction.
*/

// Use the day of the year to get a daily changing
// quote changing (z = 0 till 365)
$DayOfTheYear = date('z');
// You could also use:
// --> date('m'); // Quote changes every month
// --> date('h'); // Quote changes every hour
// --> date('i'); // Quote changes every minute
// Example array with some random quotes
$RandomQuotes = array(
  'No animals were harmed in the making of this snippet.',
  'Nice snippets',
  'The modulus operator rocks!',
  'PHP is cool.'
);
print RandomQuoteByInterval($DayOfTheYear, $RandomQuotes);