If your computer is only online for the 4 hours a day you actually use it, rather than 24 hours, that reduces your attack surface by 500%, or five times. Just as one example.
No idea why there are no firewalls that implement this, just makes sense. All the program needs is an option to insert a scheduled task to trigger this.
The decrease in online activity will be proportional to the reduction in attack surface and chances of being hacked.