Afternoon/evening in Vienna

I stayed at Hotel Am Stephansplatz--right there across from the cathedral--and a restaurant I particularly enjoyed that's on a nearby side street is Cafe Frauenhuber on Himmelpfortgasse 6-8. Very old restaurant, seemed to be popular with locals, excellent food--I had the tafelspitz and the beef was quite tender, the potatoes divine. I also like the Sacher and Cafe Landtmann on Universitatsring.

https://cafefrauenhuber.at/index.php/de/speisen-getraenke

If this is your first visit then you should go to the Sacher. That way you can experience the dish they are best known for in the right setting. If you like it and ever go back then you might try it at one of the other shops.
There are quite a few restaurants around to choose from. What sort of cuisine are you looking for? Given that you are super short on time maybe you should consider heading to the Sacher, going for your walkabout and then eating at your hotel? I have never had a bad meal in Vienna at a good hotel. It won't happen.
Even a short evening in Vienna is a great experience. With the subways you can really get around so if you want to eat far from your hotel it's not out of the question.

Ah, a one night stand with Vienna - sounds like fun :).

First, not sure when your trip is occurring, but currently a negative PCR test (valid for 48 hours) is required to eat in a restaurant or cafe, so be prepared.

Coffeehouse - Cafe Prueckel is right in your neighborhood and an all time favorite of mine. I also really love Diglas on Wollzeile, also close to your area. Sperl is not in the center and Sacher is a waste of time and money, in my opinion. Nothing but tourists and dry sachertorte. I would note that coffeehouses are not really late afternoon things in Vienna, so you might be fighting with the early dinner crowd.

Dinner - I love Puerstner on Riemergasse - very kitchy Austrian, but cute and excellent food. You also cannot go wrong with the classic Plachutta on Wollzeile - an absolute institution. Figlmueller isn't really that pricey, but it does have the best schnitzel in Vienna, accourding to locals and tourists alike. Alternatively, the same family owns Lugeck which serves similarly good schnitzel. I also really love Huth Gastwirtschaft for a slightly elevated take on Austria food. So you have kitchy, classic, best and elevated. I also have to throw in the Palmenhaus which will give you a chance to stretch your legs around the Hofburg.

Emily, you let the cat out of the bag. A Sacher Torte is indeed a big dry old cake of many layers. But, it is "a thing" and that is why it's on everyone's list to try. I have never discouraged someone from trying it and deciding for themselves. It's OK to be the tourist for a few minutes. You need to start somewhere.
Give me a Frankfurter Kranz over a Sacher any day of the week.....but this is Austria so I am going for powidltascherl without hesitation. If they do not appear on the menu, I go elsewhere. Close with a proper schnapps.

Is the sachertorte at Demel any better?

No, it is not.

But, the windows are always amazingly decorated!

Don't get me wrong - I love Demel. I just don't order the Sachertorte.

It is interesting to compare Sacher with Demel. Sacher is in a hotel and the coffeehouse is full of non-Austrians taking selfies with cake. Not really a traditional experience. Demel is a coffeehouse proper with amazing decor over two levels. Austrians tend to go to Demel to linger over cake and coffee.

IMHO the best not-dry Sachertorte you get at Aïda, the pink pastry chain, having the interior of the sixties.
I don't like Sachertorte that much, but my son, who happens to live in Vienna, prefers it from that place.

Having been to Sacher and Demel, I prefer Demel for ambiance. Sacher is an institution but not as comfortable as Demel.

Thanks for all perspectives! I'll plan to try out Demel instead of Sacher. I prefer classy to touristy!

If I could only go to one coffeehouse in Vienna, however, I would not choose either Demel or Sacher...

Emily, if it is coffeehouse of choice, then make mine Cafe Central.

Marc - Really? Are you sure? Have you been there lately to see how touristy it has become with huge lines? For me, it has to be Diglas, Prueckel or Sperl.

Emily - it has been 3 years. Has it changed that much? If so, I am saddened. It was popular before, but certainly more with locals it seemed.

I had completely forgotten about Sperl! Lovely place and on the way to the Ring from where we typically stay. I prefer its "old world" charm to that of Prückel. But based on all I have seen you post I would gladly defer to your recommendations any day! Back in October (fingers crossed)!