Set up Apache for site maintenace

We want to set up the site maintenance page from 5am to 3pm on a certain day to do database upgrade. Then we want to test the site internally before opening to the public. This is what I would do in Apache configuration:

# rewrite condition1: 5am to 3pm
# rewrite condition2: allow only internal ip
# rewrite condition3: any database driven page (".dyn", ".jsp", or ".vm")

RewriteCond %{TIME_HOUR}%{TIME_MIN} >0500
RewriteCond %{TIME_HOUR}%{TIME_MIN} <1500
RewriteCond %{REMOTE_ADDR} !^255.255.0.0*$
RewriteCond %{REQUEST_URI} \.(dyn|jsp|vm)$
RewriteRule ^/(.+)$ http://my.site.com:80/sitedown.html [L,R]