<link rel="stylesheet" type="text/css"
href="<?php $hour = date("h"); if ($hour < 12) echo "morning.css"; elseif ($hour < 17) echo "day.css"; else echo "night.css"; ?>
" />

<link rel="stylesheet" type="text/css" href="<%
if hour(now)<12 then
  response.write "a.css"
else
  if hour(now)<17 then
    response.write "b.css"
  else
    response.write "c.css"
  end if
end if
%> " />