Different css style depending on the time
Here is how I done this on this website.
First I have choose to change it by adding a class to my body, so I don't need to have many css file to do this.
And here is a PHP version to do this:
<body class="<?php $hour = date('H'); echo ($hour > 5 and $hour < 18) ? 'light': 'dark'; ?>">
this is simple if the hour on a 24 hour rang is granter then 5 and smaller then 18 it use the light class otherwise it will use the dark one!