Snowdrops are traditionally recommended to be transplanted 'in the green' ie after flowering but while still leafy. However, I believe that this is now out of fashion a as recent research refutes it. But it's always worked for me and is still practised by many growers.

I've moved daffs in growth and as dormant bulbs. Can't say I've registered much difference in the small numbers I've done.

Here is a link that might be useful: Alternative view on transplanting snowdrops

My snow drops have been next to one of my compost piles for many years. As I have used compost just about all over the garden, I have inadvertently moved snow drops just about everywhere. They seem happy where ever they turn up, and I am too. Al