itinerary for Nuremberg

The ticket machine in Rothenburg - or the DB app - will sell you a VGN Tagesticket Plus (day pass, valid all day long.) Buy it before you board your train. You can buy it a day earlier if you wish for the travel date in question, but there is no advantage. These day passes do not sell out and are not discounted if bought in advance. And advance purchase is disadvantageous since these passes are non-refundable. They permit you to ride the regional trains (which is the only way to get to Nuremberg from Rothenburg anyway.) The cost is about €25 for two persons for unlimited travel within the VGN zone on regional trains, as well as buses, subways and trams within Nuremberg.

https://images.gutefrage.net/media/fragen-antworten/bilder/459443150/0_full.jpg?v=1655930239000

The fastest route with the fewest changes to Nuremberg Hbf normally includes changes in Steinach and in Neustadt-an-der-Aisch and will require a little less than 2 hours. You can find this journey pretty much every hour of the day.... 13:09 - 14:54, for example. If you are on a tight sightseeing schedule, leave at 11:05 or 12:05, maybe, just in case there's a train delay somewhere on the way and you have to wait for the next train to come along.

https://images.gutefrage.net/media/fragen-antworten/bilder/459443150/0_full.jpg?v=1655930239000

I would just point out that a lot of visitors to Nuremberg overlook the many interesting museums there which have nothing to do with WW II. I guess that Rick Steves emphasizes the WW II things so heavily because Americans, who often know very little about Germany besides WW II, Nazis, the Holocaust, etc., are more comfortable seeing the "known" than experiencing something new and unexpected. You might wish to have a look at the other museum and sightseeing options in town as well:

https://tourismus.nuernberg.de/en/discover/places-of-interest/

https://tourismus.nuernberg.de/en/discover/museums/science-technology-museums/location/db-railway-nuernberg-db-railway-museum/
https://museums.nuernberg.de/albrecht-duerer-house
https://museums.nuernberg.de/museum-tucher-mansion/
https://museums.nuernberg.de/toy-museum
more:
https://tourismus.nuernberg.de/en/discover/museums/

We were just in Nuremberg the end of March and we did not by tickets ahead for anything. Not sure about the Art Bunker though because we did that tour through Viking (we did a river cruise after being in Nuremberg an extra 2 nights before cruise started). We loved the Germanic Museum and spent 3 hours in there. We also like the castle tour inside and the toy museum. The 3 churches inside the walls were beautiful. The Ralley Ground was disappointing and very run down. We stayed at Hotel Victoria just inside the wall across the street from the train station. You are going to have a great time.

The Party Rally grounds was disappointing. It is far less impressive than I expected. Mainly it is a park and the remains of an unimpressive looking stadium next to the Nazi Documentation Center. If I was returning to Nuremberg, I would arrive at the Nuremberg Trials Courtroom when then open and skip the Party Rally ground. I signed up for a guided tour in advance, that met outside the entrance to an underground Bunker where artwork was stored, The entrance is approximately 1/16-1/8 mile from the Albrecht Dürer Haus. Is that the Art Bunker you are thinking of? Nuremberg Castle was a good place. You can get an English audio guide at the court room building, and there are displays in another room in the building. But you probably should allow for 3 hours at the courtroom just to be sure you are not rushed. I didn't allow enough time. I skipped the Nazi Documentation center. I figured that background reading at home would take away my need for it. There is another Nazi Documentary center in Munich.

I visited Nuremberg back in the 80s when I worked for the US Army.
The Rally Grounds were then occupied by the US military. They had four sports fields inside the former rally grounds.
Still, it was possible to imagine how massive the grounds were.