By the way the book officially says (and bear in mind this is Steve Biddulph's opinion only - albeit his opinion has been developed from looking at the evidence). Take it or leave it but this is what his opinion is (and he has studied it more than I have). And you have to read the book to get the full story and see all the evidence. I can't explain it all here.
Child's first year
Do not use nursery care at all. Organise for baby to be with a parent or grandparent at all times except for occasional breaks - days off or evenings out - when you have a trusted and familiar babysitter
When your child is one
Up to one short day per week, for example 9am til 3pm, with a trusted and familiar carer. Ideally 1:1 but 1:3 at the very most.
When your child is two
Up to 2 short days per week with a trusted and familiar carer. After 2 and a half, a group setting like a good quality nursery can be suitable for girls, but usually boys are not ready until they are 3. Only use group care if the child settles well, and for half days only.
When your child is three
Up to three short days or half days a week in a good quality nursery or pre-school
When your child is four
Up to 4 short days or half days a week in a good quality nursery or pre-school
Now again, I am not saying this is practical. But there it is - his opinion based on the latest science and anecdotal evidence from people like Directors of nursery schools. And I for one cannot practically do this at the moment. I have however modified my arrangements and am now looking to sell our house, down size and give up work for a while. Not a great time to do it I know.....