Ask HN: Can I work a part-time job to start a company?

I'm saving up as much as I could to quit my job and have enough runway to build something that I could fundraise for. However, I don't want to waste a year doing petty work on the startup.

Can I work a part time job (4 hr work day), making a bit of money and having more time for my startup? or is it as draining and challenging as a full-time job?

I'm a relationship manager at a commercial bank, what kind of part-time jobs can I get?