Normally you leave daffodils in the ground from year to year. If the clump is getting too big, and there are not as many blooms as expected, then the clump will need to be split. You can do this when the plant is flowering, but you shouldn't expect them to bloom the next year. For blooms it is best to wait until the flowers are gone and the leaves are beginning to turn yellow. At that point the leaves have sent all the energy to the bulb that they are going to, you can separate the bulbs and replant.
The best time to transplant Bluebells are after they flower. If you do so before they flower, they may not flower that year due to the shock of being transplanted.
April
Summer
Yes. It is advised not to transfer them while in bloom though. You can also store them over the winter indoors. See the related link for more information on daffodils.
Soon after puberty.
The best time is after the first frost and before the last frost of your region. This is because you want to transplant when the plant is dormant.
The best time to plant most trees is during dormancy, so late Fall to early Spring is the best time to plant or transplant hybrid poplars. I feel, if you transplant around December, your trees have plenty of time to get used to their new location before new root, leaf and stem growth begin.
The best time to transplant a peach tree is January. The trees are still dormant from the winter, which will reduce the shock of transplantation. It is also best to transplant a peach tree when it is at least one year old and preferably not after they reach three years old.
Rainy season is the best time to transplant seed. During rainy season, there is a lot of humidity, hence the seed sprouts will get required good quality of water for a better growth.
At this time (December 2013), there is no indication that daffodils are transgenic plants.
Spring
Evergreens are best moved in the spring.
Early Spring where I live. Early Spring where I live.
I just read on Fox Hills Lilac Farm's website that the best time is between April and Oct. They stated that 75% are done in the fall.