Holy compounding growth! I can't believe that I just crossed the $500k invested mark in January and I'm already just one more good day from hitting $600k. I very well could cross that line in time for the end of month spreadsheet day. (Don't worry, now that I've put that thought out there, we'll certainly see a market crash)
I'd consider a CD ladder with the amount needed for each tranche maturing at the time I'd need it (depending on rates I could get compared to HYSA rates).