A function to check if date/time is in acceptable interval.

datetime_check.php

<?php
//This function checks if specified date IS IN acceptable interval from NOW to some moment in the past.
//$date_to_check need to be in classic datetime format, like in mySQL;
//$interval sets like here http://php.net/manual/en/dateinterval.construct.php, but without 'P',
//'P' will be added automatically.
function is_date_acceptable($date_to_check, $interval) {
  $now = new DateTime();
  $interval = 'P'.$interval;
  $min_acceptable_date = $now->sub(new DateInterval($interval));

  $checking_date = new DateTime($date_to_check);

  return (($checking_date > $min_acceptable_date) ? TRUE : FALSE);
}