I'm often dismayed to hear about authors who submit a manuscript to a copy editor and then wait for months for the edits to be completed. And yet I hear the same story again and again, which leads me to believe it must be a fairly common practice.
How long is too long? At what point should an author say, "Either finish it or give me a complete refund and I'll take my business elsewhere"?
Well, I suppose it's tough to make a one-size-fits-all statement when it comes to copy editing. After all, publishing houses can take six months or more to edit an average-length manuscript. But I'm talking about the typical freelance copy editor, not a large publishing house—someone like me, who has a daytime job and edits in the evenings at home.
A typical copy edit for me involves a first-round edit and a final proofread. The first round is the most time-consuming, since it involves creating a style sheet which lists character names, places, common misspellings, and other things that are unique to that author. The good thing about working with authors who write series is that most of the characters stay the same—unless you're working with G.R.R. Martin, who, in the words of my husband, "writes books with newly introduced characters who somehow manage to die thrice per novel."
Since I'm not working with Mr. Martin, my style sheet time investment pays off with subsequent books in a series, since it only needs tweaking.
After that, the rest of the edit involves the usual things: grammar, punctuation, sentence structure, the Dreaded Adverb, dialogue tags and the like. For an average edit on an average-length manuscript (55-80k words), the first round might take me about two weeks or so. Once it goes back to the author for approval & changes and comes back to me for the final proof, I usually have it in my hands again for approximately a week. That's it, unless it's a busy season when I can't edit as many days in a week.
If the book is extra long, or if the edits are heavier, add about a week to that total. And toss in a couple of progress emails in the middle of it, while you're at it—I don't believe an author should have to chase down his or her editor to see how things are going. If a week goes by, I feel I should contact the author to give an update on how things are going and where I am in the manuscript. It may only be seven days on the calendar, but I imagine it feels a lot longer to an author who has sent off months, sometimes years, of hard work to someone who may be a stranger.
I've heard (from authors I know personally) about editors who can't be reached after months, or who make excuse after excuse about why they're not done with the work. I can understand (as do the authors I've spoken with) about family issues or unexpected emergency-type things, but when someone says they "didn't start yet" after having the manuscript for a month, then goes on vacation without notifying the author they'll be gone—and still not working on it—and then makes the excuse that they just "can't get into the story," then you're getting the runaround. Copy editors don't need to get into the story. That's the job for content editors and beta readers. Copy editors look for errors. The story's enjoyability is a plus, but not a determining factor for edits.
I try to only work on one project at a time so I can focus on one story with one set of characters. For the way I work, that seems to be the most time-efficient, too. I can multitask with many household things, and I can even pat my head while rubbing my belly—what can I say? It's a gift—but when I need to concentrate, I do only one thing.
Don't ever be afraid to ask your editor how long a job should take. The time may not be set in stone, but having an estimate not only gives you a goal date, but it keeps your editor accountable to you and respectful of your time.