It's more like two business days in the academia, and only if a simple response is enough. Complex questions often take longer, because coming up with an answer may take an hour or two of uninterrupted time.

And if it's a cold email requesting something beyond a reply, and you don't have an existing business relationship with the sender, there is no expectation that you respond. An endless stream of requests from less reputable entities is an unavoidable fact of academic life. Such requests often go directly to the spam folder, as people have collectively decided that they are spam and trained the spam filters accordingly. Even if you think your request is legitimate, it can be indistinguishable from spam.