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.