Obviously they can be earlier (I read Sept-March), but they're cloud, moon and solar wind dependent. If you live at the right latitude you'll see them eventually, but planning a 1 week trip hoping to see them would be a gamble. Like I said in my post, I had to thread the needle of going at the end of tourist season when some stuff in Alaska we wanted to do was still open, but being in September so we'd have at least a hope, then I checked the moon phases to make sure it wouldn't be a full moon, too. Then I had to hope for clear skies and got very lucky. If you really wanted it you may want to keep an eye on a calendar for clear weather in Fairbanks, then grab a flight if conditions looked right. But Fairbanks is also wicked cold during the winter.