It doesn't require willpower. Write a script that warns you 10-5 minutes before 5pm that your computer will be shutting down. Then again a minute before shutdow

It doesn't require willpower. Write a script that warns you 10-5 minutes before 5pm that your computer will be shutting down. Then again a minute before shutdown. Then it shuts down. Or write one that sends a message to your partner, friends or flatmates that you'll be done in a few and to put on a kettle. Plan to have tea or what have you with your SO or flatmate at 5pm sharp. Set an alarm to take your dog out. I'm sure you can come up with other things. Add things to your schedule that force you to leave, just like your train. Even if you're in a meeting drop a "Sorry folks, we'll have to pick this up tomorrow, I have personal obligations waiting on me" and you're out.