I prefer to move them in fall while there are still remnants of their growth remaining above ground so you can tell pretty closely where they are. If you wait until you see any signs of growth in spring, you risk disturbing the rooting that has already taken place. And dig carefully!! I use a garden fork rather than a spade/shovel as it is less likely to damage the bulbs if you cannot estimate exactly where under the ground they are located :-)

Top advice, GG - that horrible feeling when you brutally hack through a whole clump of fat bulbs...grrr.