Pretty soon since most other Nightjets are now available. Check nightjet.com regularly (and book there by adding Eurail as a discount, you'll save fees and have a better overview too !).

Do you know that the Nightjet stops in Salzburg at 2am ? It won't be a very pleasant experience.

I'd recommend going to Munich or Vienna in the evening so you can get a better night sleep. Keep in mind that the departure day counts as a pass day.

Thanks, I was considering Linz as well as a departure point. Appreciate your advice 

Yes Linz would be a great choice. As long as you're not planning to take trains the next day the journey will use a single pass day.

The Nightjet sits for 2 hours in Salzburg but I don't know at what point you can board since carriages are shunted, etc.