How long do people expect to wait for an ebook once they paid?

When someone buys an ebook online, and pays for it online such as by using PayPal, how long does the customer expect to have to wait for their ebook to get sent to them? Do they expect to get it that day? The next day? Within a week?
What?
thanks Cerbus. Now i really have a question! I am thinking of selling an ebooklet online. I am a homeschooling mom, and when I pulled my kids out of school they were struggling with their reading. Now both are reading well. I wrote a booklet about the unique methods i've used to help my children be better readers.
I was discussing with my husband how long people expect to wait before they get their book. I said that i thought people expect their book right away. My husband says that is unreasonable. Nobody should be expected to sit by their computer all day long waiting for customers. I have somewhat of an internet addiction and to make a long story short, I am trying to limit my time online. I was hoping I could fill order once a week or something.
How do people get their book as soon as they pay? Is there some automatic system that just sends out the book as soon as it is paid for? Please explain.

I have ordered several books vie ebook. Never had to wait more than 15 minutes for the download to begin. The estore should be set up to deliver the product as soon as it is paid for. I always use paypal to pay for my ebooks.