When do you butcher ducks?

I hear there is a time frame... must be before a certain age or after a certain age but not in between... What? Why?

There is certain stage (not necessarity age) that you do them. The hutterites around here go out and when they can pluck the breast feathers with no blood on them that is when they are due to be slaughtered. You want it with the least amount of pin feathers coming in as possible.
We have never figured out when it the right time, we just kind of do it when it fits our schedule, meaning that most are just skinned out.