Are you saying all visas rarely take longer than a day or saying Indian visas rarely take longer than a day? I don't think it's true. Many visas can be arranged in a day , but it's not rare for them to take days/weeks.

India consulate in NY does not cater to walk-in applicants

http://indiacgny.org/php/showContent.php?linkid=200

I believe same is true for other India consulates in US