Convert a date string to UNIX timestamp and then calculate how long from now that was in the fashion of twitter.

time-ago-twitter.php

function timeAgo($dateStr) {
	$timestamp = strtotime($dateStr);	 
	$day = 60 * 60 * 24;
  $today = time(); // current unix time
  $since = $today - $timestamp;
    
  // If it has been less than 1 day since the tweet was posted, figure out how long ago in seconds/minutes/hours
  if (($since / $day) < 1) {
  
    $timeUnits = array(
	    array(60 * 60, 'h'),
	    array(60, 'm'),
	    array(1, 's')
    );
    
    for ($i = 0, $j = count($timeUnits); $i < $j; $i++) { 
	    $seconds = $timeUnits[$i][0];
	    $unit = $timeUnits[$i][1];
	 
	    if (($count = floor($since / $seconds)) != 0) {
	        break;
	    }
    }
 
    return = "$count{$unit}";
    
  // If it has been a day or more, return the date: day (without leading 0) and 3-letter month
  } else {
    return date('j M', strtotime($dateStr));
  }
}