There are a couple of schools of thought on this one. Firstly there are those who clone early to determine the sex of their plants and then there are those who wait until the donor plant is sexed before they clone.
If you subscribe to the first method then grow the plant vegetatively until it has at least five internodes before you take a clone. Make sure you label the clone the same as the donor plant to avoid confusion.
The second method requires you to take less cuttings as you already know the sex of the plant but it will be slower as the plant has already entered the early stages of flowering and any clones taken will first have to root and then secondly revert back to vegetative growth.
The bottom line is clone early and often to ensure you preserve the genetic line you are happy with.
Here is a thought from another Edge member:
Contributed by Mzzmo
keep the clones for second harvest
Take clones from the ladies, after the seedlings are sex determined(female), bud out the ladies, and while this is happening, the clones will grow and be tall enough for the second cycle, clone from those just before you induce flowering.