[Song] - Getting Dark Again

There is an Irish(?) song, I believe by the title of “Getting Dark Again”.

I have the song off of Aselin Debison’s Sweet is the Melody.

The lyrics get confusing at one point:

"… for the second time since we got up, it’s getting dark again … "

I take this to mean, that the ongoing party [The song implies dancing and drinking] is more or less a 72 hour around the clock romp. To further this belief, the song continues talking about how a majority of the party is behind them, and at best, a half hearted extension / encore of the festivities is all the guests can muster this late in the game.

What does the given lyric mean?