I ended up on the 8-year plan. Illinois required you to finish within seven after beginning, but I got a one-year extension. Part of the problem was external. I spent 1.5 years working on an experiment that didn't pan out. The second was my own damn fault. Once I did start on the right experiment, I wasted at least a year before a sense of urgency set in.
Typically, high energy physics took longer than other fields. My friends in condensed matter usually took about 5 to 6 years to finish. This was 20 or so years ago, but from my contacts in the field, I don't think things have changed that much. I interview a lot of new Ph.D's for my company, and I haven't noticed many that have taken in excess of seven years.
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind." - William Thompson, 1st Baron Lord Kelvin
"If it was so, it might be, and if it were so, it would be, but as it isn't, it ain't. That's logic!" - Tweedledee
This isn't right. This isn't even wrong. - Wolfgang Pauli