We're still collecting the surveys at the moment, which is where people tell us what their forum names are. Thus far we still have about 950 who have not sent their survey back, so I want to give it a bit of time. Maybe give it a week or so so that we catch the bulk of people before doing the first import. We'll have to do more than one import either way, since we'll have stragglers, but still.
When it comes to the other basic backer rewards like the digital wallpapers and the in-game credits, those are things we'll probably wait until May or June to do. The in-game credits I want to import only once if possible, and there are preorder people who can get onto that through the start of Early Access. Makes sense to me to do that particular thing right after EA starts and thus that window closes.
For the digital wallpapers, our art is constantly improving and we're adding more and more all the time, so I figure waiting until that period is likely to let us create the best and most exciting possible wallpapers.