I think it only lasts for an hour on random nights. Maybe you weren't playing at the time? Either that or I guess you're just really unlucky with the aurora RNG.
Yeah, it seems to only last about 50 minutes ~ usually from 9pm for me. (I say this cause it's currently 9:50 here and it just faded away for me, and I regularly see it around now.) Just make sure you check the sky every clear day around then? I've seen it atleast once a week.