It is extremely early for it, but they indeed announced that a preload should be possible right now. If OP's preload isn't working it's worth figuring out why now, so that if the issue maintains later it's not too late to have the game ready to go.
I believe the thinking behind the very early preload is so that the download servers aren't overwhelmed by the sheer number of people trying to download the game at the same time on release day. By having the preload over a few weeks it allows for a more spaced out period of time where people are downloading it, meaning less load on the servers.