Nursery v nanny is our current debate yellowwellies as when DD is one she'll need to start somewhere and 3 children at our nursery (which is absolutely fab) at approx £65 per child per day is v expensive!
Also when our eldest starts school in sept 15 we'll need to work out what to do after school on the 3 days I work. As I work for myself I am, flexible about what hours I do but I do need at least 3 full days worth of child free time to get things done.
DS1 still sometimes cries when I drop him off - especially in the run up to the birth and now she had been born. I expect he was sensing all the changes to come and it unsettled him. DS2 is usually fine being dropped off but I don't know, they are so young to be at nursery all day and maybe a nanny at home would be nicer for them. On the other hand they would lose much of the social side and I really do love the nursery and their staff.
Anyway, back to your actual question, I'd speak to the childminder as I suppose the timing will really depend on whether she has space. If she is amazing then I guess she will also be v popular and spaces snapped up quickly. If you can reserve a space for the future that's great otherwise you may just have to take a space as soon as it arises.
I'd try and avoid making the change near to due date / soon after birth as I think the extra change at that time when J will already experiencing so much change could be upsetting for him. Our nursery is making an extra fuss of A at the moment to help compensate for him not getting as much attention from me at home.
Wow that was a long post!