Afterglow

For me the song is about a group of friends or a couple who have gone to an event / a rave and had an amazing time and are currently soaking up the Afterglow of their experience. 'Even though the dancings done, don't worry cause the night is young' - Although the night may be over, it's ok because the night will live on in their memory. 'Someone pull the sunlight back, because we want this light to last' - They want to bask in the glow / the euphoric feeling that they experience after the enjoyable event for as long as possible. For me this is one of the most relatable songs in recent dance music, since going to raves and seeing my favourite artists always gives me that Afterglow feeling they are describing.

Clearly the song talks about something which about to end, and they don't want it to end :

The end of the thing described : "Even though the dancing's done Don't worry 'cause the night is young Who cares where we go"

They don't want it to end : "Someone hold the sunlight back 'Cause we want this light to last"

It could be about a long relationship, after having a good one, it's about to end, or it could be about ending of the night, which they want it to last.