Live server datetime golfing...

serverDateTime

<span id="serverDT"></span>
<script>
var nDT = <?php echo time()*1000; ?>;
setInterval(function(){
  var s=(new Date(nDT+=1e3)+'').split(' '),
    d=s[2]*1,
    t=s[4].split(':'),
    p=t[0]>11?'pm':'am',
    e=d%20==1|d>30?'st':d%20==2?'nd':d%20==3?'rd':'th';
  t[0]=--t[0]%12+1;
  document.getElementById('serverDT').innerHTML=[s[0],d+e,s[1],s[3],t.join(':')+p].join(' ');
},1000);
</script>

There is still a lot you can do to make this shorter including dropping the PHP part (this will display the client time instead of the server time).

<span id="serverDT"></span>
<script>
var nDT = <?php echo time() * 1000; ?>;
setInterval(function(){
  var s=(new Date(nDT+=1e3)+'').split(' '),
    d=s[2]*1,
    t=s[4].split(':'),
    p=t[0]>11?'pm':'am',
    e=d%20==1|d>30?'st':d%20==2?'nd':d%20==3?'rd':'th';
  t[0]=--t[0]%12+1;
  document.getElementById('serverDT').innerHTML=[s[0],d+e,s[1],s[3],t.join(':')+p].join(' ');
},1000);
</script>

Edit: Bugfix. Displays server time again. Saved 2 bytes.

@maettig Excellent. Now under the 500 mark at 489 chars (from your suggestion plus removing unncessary brackets on line 7 and whitespace on line 11).

468 chars now, but I've only really achieved that by removing whitespace. Apart from reducing var names, putting everything onto 1 line, removing indents or semicolons at line end I think this is it?

3 more chars saved by using dS=String(date).split(' ');
(instead of using toString)

@maettig It's the server DT I'm really looking to display but a lot of those changes could be used for that I believe?

Sure. I did an update to my code above.

377 chars now thanks to @maettig. Some v good changes, only drawback I can see is getting rid of the function so you see nothing for the first 1 sec and am I right in thinking those vars leak to global?

(As I understand it.... var a=1,b=2 ...b leaks to global? Or is it nothing escapes from anon functions?)

No, var a=1,b=2 does not leak. To fix the delay you can put something like <?php echo strftime("..."); ?> in the <span>. Edit: I saved another two bytes in the code above.

@maettig Mmmm OK, I'm sure someone told me doing that leaks? Oh well, learnt something as well then :)

Don't mind the delay (gives the appearance of actually linking in with the server) ;)

Am integrating this as a final solution into ICEcoder today. Many thanks!

I know you're aiming for a specific format but why not let the end user in control and use the locale Date format ?

<span id="serverDT"></span>
<script>
var nDT = <?php echo time() * 1000; ?>;
setInteval("document.getElementById('serverDT').textContent=new Date(nDT+=1e3).toLocaleString()",1000);
</script>

@p01 Good point. I chose that format because it looks a little nicer than the regular Date output. In the bigger scheme of things I don't mind the extra 100 bytes or so on my IDE to have this format.

@maettig Good spot, updated.