Do you have other plans for the day? It would be a good afternoon to do Andrassy ut. Start with an early lunch at Hachapuri Restaurant at the end of Andrassy ut. Maybe 11:30 to 12:30. Yes, its Georgian, but you came to Budapest for exotic so this is the best bet on Andrassy ut. After lunch walk up Andrassy ut to the House of Terror. Sorry for the name, but it really is an outstanding museum based on the horrors of fascism in Hungary in a building with a very interesting history and a Soviet tank in the courtyard..
Aterwards get on the metro at Vorosmarty utca, then off at the next and then walk to the next and get back on and get off at the next. This way you can see a pretty good cross section of the stores, mansions and embassies along the Champs-Élysées of Eastern Europe. Your last exit from the M1 Metro (the oldest metro on the continent of Europe) will be the Hősök tere stop. This is Hero’s Square. See Hero’s square and walk to the Széchenyi bath house. Now soak and play until 7:00. Did I mention that you were carrying swim suit and towell? At 7pm head over to your reservation at Paprika Vendéglő down the street from Hero’s square - excellent authentic Hungarian food in a great atmosphere: relatively inexpensive. At about 8:15 you want to be on your way to the concert which is just a short walk away.
The concert should be over about 10:30 so head to the M1 to the Opera station, get off and make the 5 minute walk to your reservation at Kadarka’s wine bar for a night cap before heading home.
A day well spent.