Are you sure that's not local ordinance somewhere? Everything I've purchsed in the SF Bay Area in the last 3 years has been a 10 day waiting period (which is still 10 days too long).Well, let's see...
California has also had a waiting period for handgun sales since at least 1923. The California Legislature increased the handgun waiting period from one to three days in 1955, to five days in 1965, and to the current 15 days in 1975.
Your link cites data that stops at 1990. I started buying firearms in Calfornia in 1999 and the waiting period was 10 days. It is still 10 days.