Although qBittorrent has a built-in scheduler, but currently it does not provide any way to schedule for program exit or even to set download limiter to 0KB/s. See issue #6020.
However one can use Windows Task Scheduler and command line to achieve the same goal: Here is how: (I'm using qBittorrent v3.3.13)
Disable any prompt that requires user interaction during exit:

- Goto Tools > Options > Behavior > Desktop
- Uncheck "Confirmation on exit when torrents are active."
- Also uncheck "Close qBittorrent to notification area." (We want it to quit, not just minimize itself.)
Schedule a task for automatically exiting qBittorrent:
- Press
Winkey + R, type taskschd.msc, and press enter. (Or find and open task scheduler from the start menu.)
- Click on "Create basic task..." link and fill the form...
- Choose to "start a program" as action.
- "Program/Script":
taskkill
- "Add arguments":
/im qbittorrent.exe
Linux users should be able to do the same using the kill command and crontab. Or have a look at Is there a workaround for a lack of scheduler in qbittorrent? on Linux & Unix Stack Exchange.