I've refered this website here before, it's the best example i've seen of this ever :)

Nodster, where should I put the hreff's of my morning, afternoon, evening, night styles? I did't found that :(. So can you help me ?

/*
* Switcher to switch the stylesheet based on the referring url. for
* instance, you can select a custom stylesheet based on if the visitor
* is coming from google or digg.
*/
referrerSwitcher : {
strategy : "stylesheet",
targetId : "style_target",
defaultStyle : "referrer.css",
// Feel free to change this as you wish, the key is a regular expression and
// the value is the css file to use.
styles : {'/digg.com/' : 'digg.css',
'/stephenminded.com/' : 'sm.css'},
getStyle : function () {
var ref = document.referrer;
for (var i in this.styles)
{
var pattern = new RegExp(i);
if (pattern.test(ref)) return this.styles[i];
}
return false;
}
},

/*
* As the name suggests, this does the work of switching the style. It
* takes a Switcher object which conatains the strategy by which you want
* to switch the style as well as the function to call which returns the
* value that the style should be.
*
* Details about the switcher object:
* General structure:
* var switcher = {
* strategy : String,
* defaultStyle : String,
* target_id : String, (only used when strategy=='stylesheet')
* getStyle : Function
* }
*
* Description of fields:
* switcher.strategy - a string containing either "id" or
* "stylesheet". When 'id' is specified, the script will change
* the id of the body element to the value returned by getStyle.
* When 'stylesheet' is specified, the script will grab the
* element whos id is defined in target_id and set the href to
* the value returned by getStyle.
* switcher.defaultStyle - a string which represents the style you
* want set if the getStyle function fails.
* switcher.targetId - used when strategy is 'stylesheet', this is
* the id of the stylesheet element you wish the script to change.
* switcher.getStyle - this is the function that decides which
* style should be set. it should return a string or false if
* you want to use the value defined in defaultStyle.
*
* For an example of the switcher object, look at referrerSwitcher and
* timeSwitcher above.
*
* @param switcher
*/

P.S sorry for such a long post :oops:

Nodster, thank you very much man :)

When I tryed to install the latest script, I saw that I can't do it with WordPress CMS, so I thought that I just need to change the header according the time, so I made a very simple PHP script :P.

$hour = date('H');

if ($hour < 8) {
echo('<div id="header_n"> </div>');
} elseif ($hour < 21) {
echo('<div id="header_d"> </div>');
} elseif ($hour < 24) {
echo('<div id="header_n"> </div>');
} else {
echo('<div id="header_d"> </div>');
}

Thats all :P, but really thank you very much man :)