I think I get it - here's my explanation of how I understand the calculation:

225,000 Savings

4% SWR

9,000 yearly

750.00 monthly 12

173.08 weekly 52

24.66 daily 365

1.03 hourly 8,760

So to earn $1/hr in retirement using a 4% SWR, you need to save $225K. Using that logic, to earn the minimum wage for 24 hours a day in retirement you need to save $1,687,500 ($225,000 * 7.50).

I don't actually know what the minimum wage is, but $7.50 is close right? I also assumed a 24 hour day, and no one works a 24 hour day, so YMMV.