Earlier quoted context omitted.
Yeah I understand how it works (I have done postgraduate research) - I didn't know you were including undergraduate/postgraduate studies, I thought you were meaning thesis only!
Err, I wasn't including undergraduate, just graduate. At least at the schools I know about, there isn't really much of a distinction between "thesis" time and PhD time generally. There's quals, but they aren't that important at a lot of places. Mostly if people say "I'm a 4th-year PhD student", it means they entered the program 4 years previously. They probably spent most of the first two years taking classes, though…
Good guess. Where I'm from you can start on your phd work in your fifth year of study normally (for some earlier), and it takes 2-3 years after that to complete your project + thesis.