karthik:
Sure there is ...
True, another system needs to be "on" ... but then again, that could be the same system you have suggested using with the "at" command. And yes, the limitation is that my script runs on WinXP (as opposed to Linux, etc) -- but it should also work all the way down to Windows 98.
By using Windows TaskScheduler you can set up a job to shutdown your NASLite system at a regular point in time (including when you log on or when the system starts). There is no obvious option to do so together with your shutting down your Windows system, but then again you might not want to do that because it would be executed every restart as well. Or you can click on a shortcut on your desktop which executes my script just before you go to sleep. (Or you can let Windows TaskScheduler shut down your NASLite first, then shut itself down ! I have done this before.)
My main desktop has a RTC (Real Time Clock) option in the BIOS which I set up to power up the system every morning at 07:00. On that one computer I use Windows TaskScheduler to do all sorts of other things, including turning on my Internet Server (a firewall and web-filter system) at 7:03. You get the idea ...
Does that help ?

Georg