The PS5 hits 20m units after 18 months and 22 days (568 days).
For reference, the PS4 sold 20m units in 15 months and 14 days (471) days.
As noted by industry analyst Daniel Ahmad on Twitter, the PS5 hit 20 million units in one year, six months, and 22 days (568 days in total) meaning it’s fallen slightly behind the PS4’s record of hitting 20 million units in one year, three months, and 14 days (471 days in total).