The point about young teachers entering the profession is interesting - but to refer back to Teach First, for example, the often quoted statistic of 40% leave within x time isn't accurate. It's about 10%. Of them actually still in teaching after 5 years. The burn out rate is massive.
As to the hours, I think it is more useful to look at it the other way round. There are 120 hours in a 5 day week. (24x5) An ordinary classroom teacher is in front of the class for 21 hours. (99). Lesson planning, for those 21 lessons - well, let's say 10 minutes a lesson (those of us who do it know that it is far, far more than that, but for the sake of argument, let's say 10 mins) about 3 and a half hours (95.5).
Marking - two kinds, book marking - say 5 mins per book per week (lets say 5 classes, 25 students in each) about 10 and a half hours (85) and then marking of homework, assessments, GCSE Controlled Assessments, spelling tests etc (again, a guesstimate - obviously GCSE marking takes longer, there are 'heavy' marking periods round exam and assessment time - my school has 6 assessment periods a year for major pieces of work plus a piece of homework every fortnight) so maybe 10 minutes per student per week - 21 hours (64). (Supposedly) only 1 meeting a week - (63) - paperwork; IEP reviews, reports, data input, positive and negative incident record keeping, awarding housepoints, exam entries, etc etc - maybe 2 hours (61) tutorial/registration time (in my school, 20 minutes a day) so another hour and 40 minutes (59 hours 20 minutes)
Actually talking to students - detentions, break lunch and after school, listening to problems, mentoring, 121 intervention, answering questions about homework, answering emails from students resolving difficulties, etc etc, GCSE after school sessions - let's say 4 hours (55 hrs 20 minutes) duty (55 hours) travel to work; for me 30 mins each way (50 hours) communicating with parents - meetings, phonecalls, emails, postcards (48 hours) tidying up and maintaining the classroom environment, (47)...and that is without parents evening, drama performances, planning trips, performance reviews, chasing homework and permission slips, and perhaps most significantly, trying to retrain myself constantly for the next round of changes to the exam criteria -
So I have less than 9 and a half hours a day left to eat, sleep, go to the bathroom, shower, dress, shop, play with my own DC's, cook, clean...clearly not do-able but each hour I spend on anything else is another hour of the weekend and holidays.