I think it's up to the individual couples as to how much time they spend in training.
To learn a completely new dance each week, especially for beginners, I dont think an 8 hour day is excessive - as has been said, no more than going to do most normal jobs.
And - in reality they have limited time.
They dont start until Monday afternoon - and for the couples who are appearing on ITT on either Monday or Tuesday, this means only an hour or two of training on Monday.
Then - in theory - they get 3 full days, Tues, Wed and Thurs - but this can be interrupted with other media commitments and stupid VTs.
Friday and Saturday they are at Elstree where they can't train continuously because they need to share times on the floor with the other couples - plus they have costume fittings etc....and on the Saturday there is make up and costumes.
I seem to remember, in years gone by, that some couples also trained on the Sunday, but have not heard of that happening this year.