I've not had the opportunity to shoot aurora (yet) but have done some other night time stuff (stars). Shutter speed is going to depend on aperture, obviously. For night timelapses, you really can't close the shutter down like you do during the day. A lot of it is going to be done wide open, or close to wide open. You're shooting, generally for aurora, with wide angle lenses focused at infinity so depth of field isn't really a concern even shooting wide open. You're going to be looking, more probably, at shutter speeds in the 10 to 30 second range, ISO settings in the 800 area and apertures from 1.4 to 2.8. When I've done stars (aperture doesn't matter in this case) I've generally shot around 30 seconds at ISO 800.
If you haven't already found it, the forum at timescapes.org is a great resource. The forum at lrtimelapse.com is also good. The LRTimelapse plugin is good too.