Tl;dr: Can you use down time at work to build a side gig or passion project?
I was in a similar situation last year (well, it had been building). Great job, top pay, 5 years out from FIRE. But I think I have a 7-year itch in general when it comes to jobs: That’s about how long it takes me to cross over from full mastery/indispensability to eye-stabbing boredom. (The job came with a long commute, though, so I should note that the decision was a little easier, since I switched to working at home — but for far less money.)
Anyway, in my secret (even, I think, to me at first) transition, I started using my extra prep time at work to do my side gig. This was after I was already done with everything I could do at The Job (for the day, for the week, etc.), and my side gig was writing, so you can just pull up a different window and make it happen.
After a year or so of gigging, I went to my boss and asked for the reduction in hours to 3 days per week. I got it (indispensability). Did that for another 6 months or so before giving notice, because by then I was confident that my freelance writing business was enough.
I did give up the 5-year FIRE plan to work from home, but it’s so much freedom that it was worth it for me. I still have to work, but I call an awful lot of the shots, an success to me feels like being able to turn down writing jobs I don’t want because they’re boring. If I hadn’t bee plugging away at it during my downtime at The Job first, though, it would have taken me much linger to feel like I could quit all that income and change my FIRE plan.