Postgres Date Type Value

Want to retrieve a date type from a postgres table using libpq
PQexecParams() in binary mode (please humor me).
https://www.postgresql.org/docs/14/datatype-datetime.html says that a date
is 4 bytes (4713 BC to 5874897 AD). src/include/utils/date.h defines:

typedef int32 DateADT;

Something like this:

int32_t date_val = be32toh(*((uint32_t *) PQgetvalue(res, 0, 17)));

Gives date_val=1,466,004,328 for 2022-10-25.

Since 4713BC is the start of the Julian calendar thought it might be a
simple day count but the value is too large (2,459,878 days from 1 Jan
4713BC to 2022-10-25). So clearly not a day count. My simple maths gives
me 585.966... ticks per day.

How do I interpret the 4 bytes of postgresql 'date' value?