Normally 3-4 months. LR is released on a regular schedule. When a new camera is released between the LR releases, the update for the camera is normally in the first full cycle after the camera goes public. In this case you are probably looking for LR 6.0.1 which will be after the upcoming 6.0.0 release.
As a work around, you can use Nikon's software to convert the NEF files to TIF or JPG, then import those into LR. (Or shoot raw+JPG.)