I got this php script and I works perfectly:

<img src="http://www.lasvegascity.nl/wp-content/themes/atahualpa/images/header/header_<?php
$hour = date('Hi'); // hour of the day, 24 hour clock
if ($hour > 1759 or $hour < 600) {
$timepic = 'night';
} elseif ($hour > 1200) {
$timepic = 'day';
} else {
$timepic = 'morning';
}
echo $timepic;

?>.png">

But when I change <?php echo bfa_header_config(); ?> in header.php, the menu wil disapear. Where can I put this php code so my menu won't disapear?

If you are using this to replace the header image here is what you do
1) install the plugin 'exec-php'
2) at ato->Style & edit HEADER AREA->Configure Header Area replace %image with

<?php bfa_widget_area('name=header_image_area'); ?>

3) go visit the home page (this causes the widget area to be created
4) go to dashboard->Appearances->widgets - there should now be a widget area 'header_image_area'
5) add a text widget to this area
6) put your code in the text widget
7) optional - style it

that's it.

Yes you are great! Thanks...

The greatest thing is, when I update the ata theme, the code will not change...