It depends. I think that MSFT comes out with updates once a month (the 2nd Tuesday of each month) unless they have some really screwed up stuff come up, If you just check for updates on that Wednesday, you’ll be OK.
Update: If you are going to use Automatic Updates to makes sure to tell it that you only want it to download the updates for you and let you install them. I think that Windows will automatically restart your PC if you allow it to download and install the updates without your intervention.
Here’s a little write up on Automatic Updates.