Computer Restart Resets My Steam Downloads?

I am trying to download the new Batman. However with the file size being 35GB it will take me a while to download this.

The problem I am having is when I shutdown my pc the download for Batman resets back to about 5GB downloaded each time. I'm not sure if this could be due to me using a shutdown timer that I downloaded so I could leave my pc going for a few hours after I go to sleep?

I've looked at the other things posted on this forum but cant seem to find a solution.

Anyone have any ideas?

There currently is no such option in Steam. However, there is a petition/idea going on on the Steam Forum.

Something you can do, is to switch your computer off after a set amount of time. For example, if the estimated time is still two hours when you go to bed, you can make it shutdown after three hours (for security). To do this, run the following command (by pressing windows button + R:

shutdown -s -t 10800

the number is the number of seconds it waits before it shuts down. Cancel this timer by running shutdown -a. More information here.