PHP date comparison

e.g. via strtotime and time().
The difference must be less then 86400 (seconds per day).

<?php
echo 'now: ', date('Y-m-d H:i:s'), "\n";
foreach( array('2008-02-16 12:59:57', '2009-12-02 13:00:00', '2009-12-02 20:00:00') as $input ) {
  $diff = time()-strtotime($input);
  echo $input, ' ', $diff, " ", $diff < 86400 ? '+':'-', "\n";
}

prints

now: 2009-12-03 18:02:29
2008-02-16 12:59:57 56696552 -
2009-12-02 13:00:00 104549 -
2009-12-02 20:00:00 79349 +

only the last test date/time lays less than 24 hours in the past.

Just adding another answer, using strtotime's relative dates:

$date = '2008-02-16 12:59:57';
if (strtotime("$date +1 day") <= time()) {
    // Do something
}

I think this makes the code much more readable.

if ((time() - strtotime("2008-02-16 12:59:57")) < 24*60*60) {
  // less than 24 hours ago
}

if (strtotime("2008-02-16 12:59:57") >= time() - 24 * 60 * 60)
{ /*LESS*/ }