That answer all depends on you and the person who is reading for you. And it varies even then. I do some beta reads and sometimes, I can zip right through in about 3 days. That is when my work load is light and I'm not actively working on my own WIP. It all depends on what you want the beta reader to do. If he/she is doing a line-by-line, it may take a while. If you just want a reader to give an opinion of the story, it shouldn't take too long. But there again, it all depends on the betas time schedule.
As a beta reader, I have no problem if the writer sends me an email like, "how's it going?"
I just save what I've done, let the writer know that I'm not finished and send it back. I still continue working on it, but as a writer, I like to know progress, too. The first couple of chapters are always the toughest for me and that's what I usually get the most feedback on.