I am a part time student and I am in the UK, so I don't have classes. My supervisors recommend I spend 15-20 hours on my studies currently (next to a nearly full-time job).
Of this time, I find that admin, form-filling, contacting people and all that stuff can easily take 3-4 hours each week. That then leaves 16 hours at best.
As I do not have classes, I have to find other ways of getting input on how to do research. A combination of seminars, conferences, supervision meetings and a number of MOOCs and online webinars takes up on average 6 hours a week.
This leaves 10 hours.
Of those, working on a couple of papers for conferences takes up another 2 each week. Contacting people and setting up research interviews currently takes about an hour, while working on my research database and research design takes another hour each week at the moment (this kind of just has to fit in).
That leaves 6 hours for reading. At my current speed, I manage about 10 pages an hour if it is difficult, or around 30 pages an hour if it is fairly easy overview material. Now, that gets me to around 120 pages a week, which is nothing and it worries me. I feel that I should be reading 500 pages a week. But it is a question of 'how long is a piece of string' as there is always more to do, more that I could delve into... As my topic is interdisciplinary, there's no real way of determining when something is enough.
However, let us say I take 5 weeks of holiday in a year, that then means at the end of a year, I will have read around 5500 pages (only). This doesn't sound realistic to me. That's only 11,000 pages over a full year of studies. The introductions I have on my desk already cover about half of that. Then I have an equal amount of articles and book chapters, and this is before I do any serious searching in great detail. On the other hand, getting much above 40,000 pages and it starts getting ridiculous the other way around, but I have a feeling that I should not be able to write a PhD based on only 50 pieces of work.