"Do you know when the dance is?"
Translation:¿Sabes cuándo es el baile?
Duolingo is using 'es' from the verb ser with times such as when a movie, game etc starts. It's using "está' from the verb estar for locations. That's the correct use from what I get from the language guide on the use of ser and estar on SpanishDict!.com. https://www.spanishdict.com/guide/ser-vs-estar
my understanding is when something that is fixed and constant, we use SER. when something that is subject to change, we use ESTAR. however, location etc, we use estar, even it does not change often. Here, as you mentioned, the time for start of game, movie etc, it is not changing whence the time is determined, but in a lot of situations, it is not always clear which of the two words should be used. If a mistake were made, I do not feel it is big deal when we are talking in every day life, as long as another party understands. DL is just teaching the right way as much as it can.
Bailer (infinitive) means To dance.
El baile (noun) means The dance.
When you place a definite article before a form of an infinitive you are no longer using it as a verb, so you will not be conjugating it.
I realize you've probably moved on from the question here, but I'm posting this for anyone else who may have the same question.
Because you used the word for "where" (dónde) instead of the word for "when" (cuándo).
One more note: estar is used for location except for the location of events, when you use ser. So if you were asking where the dance is, you would say "dónde es el baile", since the dance is an event.