im = in dem. Wo? In dem Stadion. Das Stadion.
Sein letztes Konzert gibt er am 24. April. This is present tense but talks about the future. Not the last concert he played but the last on in his current tour, which he is yet going to play. But in German we avoid using the future tense if there is something else which indicates that it is future. Here, the date is sufficient. I can say "ich gehe in dreißig Jahren in Rente" and it is still present tense, even though it talks about what is going to happen after thirty years.