Apache’s mod_rewrite can be used to serve pages depending on the time.
RewriteEngine on
RewriteCond %{TIME_HOUR}%{TIME_MIN} >2300
RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
RewriteRule ^index.php$ day.html
RewriteRule ^index.php$ night.html
When request for index.php is made then to corresponding time day.html or night.html page is served.