I just bought the Lumie Elite, and have been using it as a reading light at night. You can put it on with no timer, but you can also set it to dim over a period of time (say, 30 mis).
So what I do is read until I get sleepy, then click the alarm-on button. 15 mins later it is starting to get dark in the room, so I put the book down and drift off (hopefully) over the next 15 mins.
Yes. The sunset only starts when you turn on the alarm. You don't even have to have a sunset - you could just turn on the alarm and turn off the light as normal when you're ready to sleep.