The arbitrary 8.5-9 hour workday drives me nuts, because a lot of the time, I really only have 3 or 4 hours worth of work to do. I generally work quickly and I value my time. Can I make a decent living doing something that gives me this kind of flexibility?
Find something that is based off deliverables or project completion rather than time at your desk. Maybe contract work or freelance. Maybe run your own business. Another option is remote work.
The standard isn’t just a few hours a day though so you’ll likely have less pay than you might otherwise. Also if you’re just an employee you’d be working part time so no benefits either. This probably wouldn’t be decent pay, especially if you want to save money while also paying for things.
If you are your own boss you could decide to work less but generally it’s a lot more work to run your own business. The business and freelance work would both have the issue with a lack of benefits.