I think as per some PP it depends on the child, if they are currently in nursery for full days all week, they yes will be tired, but they are already used to longer days.
I have 2 in school and since day 1 they have done 4 breakfast and after school clubs a week, and since the start of this term it's breakfast club all week now and the 4 after school clubs.
They are ok with it, more so as they have always done it.
I would maybe sign them up for all week (places can be like gold dust) trial it with maybe every so often you take to class or pick up from class (work allowing) and see how they get on, at first they will be tired, but that will also be down to a change of routine, new ways of learning etc, but you might find that they really like the extra hour or so with friends.
Mine often moan I pick them up too early as they haven't finished a game or got their snack ha!
Don't forget if the is ofsted registered and you are eligible, you can use the Tax Free Childcare to pay and recoup 20% of the fees,