how to display time until or time since a specified date javascript or php

Basically开发者_如何学运维 I need to display how much time till a specified time or if its passed, how much time since it passed.

The original string would look just like this: 07/20/2011 01:13 am

EDIT: switched from doing conversion in javascript to php:

//get local time in UTC format
echo gmdate("Y/m/d\TH:i:s\Z");
  echo '<br />';

 //convert time to UTC
  $the_date = strtotime("07/20/2011 01:13 am");
  echo date("Y/m/d\TH:i:s\Z",$the_date);

Doing the above gives me these to work with:

//local time
2011/07/20T19:49:39Z
//specified time
2011/07/20T01:13:00Z

How can I take the specified time, and the local time and make it display something like these examples:

Started 36 mins ago
Will start in 33 mins
Will start in 6 hrs 21 mins
Will start in 4 days 4 hrs 33 mins

And if you want to do it in Javascript, it is slightly more painful but you get the benefit of a "live" countdown.

Here's a great breakdown of how to do that.

http://ditio.net/2010/05/02/javascript-date-difference-calculation/

See the manual. The example #3 with the use of datediff will help you too.