Is there any way to schedule software update?

If you goto the Software Update preferences, you can set it to daily, monthly or weekly. Obviously, this a very basic update scheduler. If you want to update weekly at this time just goto preferences and select weekly, now.

You can also do it using an Apple script + softwareupdater as described here.

Emmy - if you want to automate this without a user approving the changes, see this thread. How to silently update OS X and reboot if necesary?

Otherwise just use iCal to schedule and set an alarm to open the file

/System/Library/Core Services/Software Update.app

as shown below:

There are tons of ways to script this, but iCal is really simple for this task.

You can automate this by date and time using 'launchd' here's an article about it. Note: This will download the updates in the background automatically, you won't see the apple software update window. So you won't have to push any confirm to install buttons.