Translation:They are giving the date and the time.
In real life? Context. And sometimes (when the verb starts with a vowel), there's a liaison to help. Elles arrivent ("elle-z-arrive"). With a lot of irregular verbs, the verb will tell you that it's plural. Elles sont, elles peuvent, etc. However, with many verbs, in many Duolingo exercises, it's impossible to differentiate between elle/elles and il/ils.
In general, many singular/plural pronoun-and-verb combos sound identical. There is no phonetic difference between "elles donnent" and "elle donne" (or elles portent and elle porte, elles mangent and elle mange). However, when the verb starts with a vowel, there is a liaison that will tell you it's plural. "Elles arrivent" sounds like "elle-zarrive," while "elle arrive" sounds like "elle arrive," and "elles aiment" sounds like "elle-zaime," while "elle aime" sounds like "elle aime." Sometimes there are other clues, like when you hear "leur/leurs" instead of "son/sa/ses." Elles mangent leur gâteau. They eat their cake. Elle mange son gâteau. She eats her cake. Usually, in the real world, it's relatively clear from context.. .