Very old hat to shut a site down for maintenance unless you are still in an early development cycle.
Also, the down time could be very hazardous to your search listings as I do see the bots coming through a fair bit, and down time like that has a big impact as you have changed the whole site and the bot thinks the site is different and resets the ranking.
Could try and run a mirror database then merge and test any additional files you are adding on a test folder or locally.
Man, one of my sites had to shut down for maintenance then it would be down 20 hours in 5 days (we did work this out). So we just used a process which mirrors then updates. Easy stuff
