You can book immediately when you found out you are pregnant if you have one in mind already. Popular confinement ladies are normally quite fully booked and you need to act fast. If you unable to find a good confinement lady or decide to have one in the very last minute, you can book through confinement agency such as PEM. PEM has free replacement of CL if you are not satisfied with the CL.
As soon as you find out you're pregnant especially if the nanny you have in mind came highly recommended from someone. Most nannies are engaged for a full straight month, so that only makes them available 12 times a year assuming that she is not taking any time off.
Would suggest that you start looking around and try booking in your early stage of 3rd trimester
I started looking for one once I passed my 1st trimester and many were already taken.
thanks