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.
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.