Have you ever visited website and had no idea what the person was selling or what they were wanting you to do next? I have, and it is a percent frustrated at 100. It is a time waster and an immediate turnoff. I can't hit the back button fast enough.
If I told you Google defines a fast loading web page as 3 seconds or less, would you be surprised? Probably not, that seems reasonable. Who would wait that long, right?