Dear madabouteu,

I believe the general guidance is to dig them up right after their leaves have dried up. You might want to mark them so you don't loose the clump. I believe this question has been answered many times. Try searching "dividing" and see if you can't get a great deal of information.

That is the CW, but I usually move them when I feel like it & can see the foliage well. Not had any problems with re-bloom by doing that, moved many Daffs, at many diff times.

I'd normally also move after the leaves die back, but I have also done it after the blooms but the leaves are still green and doing well. I think because it's a bulb, it has a little bit more tolerance for transplanting, even while leaves are up. As a result, I was successfully able to transplant and in the following spring, had some blooms from the daffodils which had not been blooming previously for several years.